HIV Glossary — Plain-Language Definitions

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340B Drug Pricing Program (340B): A federal program created in 1992 that lets clinics and hospitals serving people with low incomes and people who are uninsured buy outpatient medicines at discounted prices. Drug makers that take part in Medicaid must sell covered drugs to these "covered entities" at or below a set ceiling price. HRSA runs the program, and savings often fund HIV services. Source: Congressional Research Service

A

ACA (Affordable Care Act) HIV Provisions (ACA; Obamacare): The health care law that made coverage easier to get and keep for people living with or at risk for HIV. Insurers cannot deny or drop coverage because of a pre-existing condition like HIV; Medicaid expanded in participating states; and Marketplace plans, tax credits, and required preventive services make testing, prevention, and HIV care more affordable. Source: HIV.gov
Acute HIV Infection (Primary HIV infection; Stage 1 HIV): The earliest stage of HIV, roughly the first 2 to 4 weeks after the virus is acquired, before the body has made enough antibodies for an antibody test to find them. HIV multiplies quickly during this time, so the viral load is very high and HIV passes easily. A viral load test can detect it before antibodies appear. Source: NIH Clinicalinfo
ADAP (AIDS Drug Assistance Program): The AIDS Drug Assistance Program is a federally funded program that provides HIV medications and other HIV-related services to people with HIV who have low incomes or who are uninsured or underinsured. ADAP services are available in all 50 states and the U.S. territories, and each state runs its own program with its own enrollment rules. Source: NIH Clinicalinfo HIV Glossary
Adherence: Taking your medicine the way your care team explains it — the right dose, at the right time. Good adherence to an HIV regimen keeps the virus suppressed, lowers the chance of drug resistance, protects your overall health and quality of life, and means you will not pass HIV to a partner through sex. Source: NIH Clinicalinfo HIV Glossary
AIDS (Acquired Immunodeficiency Syndrome; Stage 3 HIV): AIDS is the most advanced stage of untreated HIV. It is diagnosed when HIV has weakened the immune system enough that a person has an AIDS-defining condition, or a CD4 count below 200 cells/mm3. With today's treatment, many people diagnosed at this stage recover their immune health and live long lives. Source: NIH Clinicalinfo HIV Glossary
Antibody (Immunoglobulin): A protein your immune system makes in response to something it recognizes as foreign, such as a virus. Antibodies attach to that target and help destroy it. Many HIV tests work by looking for HIV antibodies in blood or oral fluid rather than looking for the virus itself. Source: NIH Clinicalinfo HIV Glossary
Antigen/Antibody Test (Ag/Ab combination test; combo test): A test that looks for two things at once: HIV antibodies and HIV-1 p24 antigen, a protein from the virus's core. Because it catches the antigen first, it finds HIV earlier than antibody-only tests — usually 18 to 45 days after exposure with a blood draw. This is the standard lab screening test in the U.S. Source: CDC
Antiretroviral Therapy (ART) (HIV treatment; combination therapy; HAART): The daily use of a combination of HIV medicines — called an HIV regimen — to treat HIV. A first regimen usually includes three antiretroviral drugs from at least two different drug classes, and today those are often combined into one pill. ART is recommended for everyone with HIV, starting as soon as possible after diagnosis. Source: NIH Clinicalinfo HIV Glossary
Apretude (cabotegravir extended-release injectable (CAB-LA for PrEP)): A long-acting injectable form of cabotegravir, FDA-approved on December 20, 2021, as an injection for HIV prevention. It is a PrEP option for people who would rather get a shot on a schedule than take a daily pill. Source: NIH HIVinfo

B

Baseline Testing (Baseline labs): The first set of lab results after an HIV diagnosis, used as the starting point everything later is compared to. Baseline testing includes a CD4 count, a viral load, and resistance testing. These results guide the choice of your first regimen and show how well treatment is working over time. Source: NIH Clinicalinfo
Biktarvy (bictegravir/emtricitabine/tenofovir alafenamide (BIC/FTC/TAF)): A single-tablet HIV treatment that combines three medicines — bictegravir, emtricitabine, and tenofovir alafenamide — in one pill taken once a day. The FDA approved it on February 7, 2018. Combination pills like this lower the number of pills a person takes daily, which can make treatment simpler to stay on. Source: NIH HIVinfo

C

Cabenuva (cabotegravir/rilpivirine (CAB/RPV)): A long-acting HIV treatment given as shots instead of daily pills. It combines two medicines, cabotegravir and rilpivirine, as extended-release injections, and the FDA approved it on January 22, 2021. Injectable treatment is not the right fit for everyone, so your care team will talk through whether it suits you. Source: NIH HIVinfo
Capsid Inhibitor (Lenacapavir; Sunlenca; Yeztugo): The newest class of HIV medicines. Capsid inhibitors interfere with HIV's capsid, the protein shell that shields the virus's genetic material and the enzymes it needs to copy itself, and they can disrupt HIV at several points in its life cycle. Lenacapavir is a capsid inhibitor, FDA-approved for treatment (Sunlenca, 2022) and for prevention (Yeztugo, 2025). Source: NIH HIVinfo
CCR5 Antagonist (CCR5 inhibitor): A class of HIV medicines that covers the CCR5 coreceptor — a doorway on the surface of some immune cells, including CD4 cells — so HIV cannot use it to get in. A test can show whether a person's HIV uses that particular doorway before this medicine is prescribed. Source: NIH Clinicalinfo
CD4 Count (CD4 cell count; T-cell count): A lab test that counts the CD4 T cells — key immune cells — in a sample of blood. For people living with HIV, the CD4 count is the most important measure of immune strength and the best predictor of how HIV is affecting the body. It is also used to see how well treatment is working. Source: NIH Clinicalinfo HIV Glossary
CD4 Percentage (CD4 cell percentage): The share of your lymphocytes (a type of white blood cell) that are CD4 cells. In some situations — for example, in children with HIV under 5 years old — the CD4 percentage gives a clearer picture than the CD4 count of immune health and how well treatment is working. Source: NIH Clinicalinfo HIV Glossary
Clinical Trial (Interventional study): A research study that tests whether a new medicine or other approach is safe and works well in people. Volunteers join clinical trials to help find better ways to prevent, diagnose, treat, and understand illness. Trials run in phases, and people living with HIV have shaped nearly every advance in HIV care by taking part. Source: NIH Clinicalinfo HIV Glossary
Coinfection: Having two or more infections at the same time. For example, a person living with HIV may also be living with hepatitis C, tuberculosis, or both. Coinfections are common, treatable, and worth screening for, because treating them together protects your health. Source: NIH Clinicalinfo HIV Glossary
Comorbidity (Comorbid condition): Having two or more health conditions at the same time — for example, living with HIV along with high blood pressure or diabetes. Because HIV treatment now supports long lives, much of HIV care today focuses on managing comorbidities alongside HIV. Source: NIH Clinicalinfo HIV Glossary
Condomless Sex: Sex without a condom. This used to be called "unprotected" sex, but that language is out of date: PrEP and an undetectable viral load (U=U) are effective HIV prevention on their own. Condoms still matter, though, because PrEP and U=U do not prevent other STIs. Source: aidsmap
Confirmatory Test (Supplemental test; follow-up test): The second test that follows a reactive HIV screening result. In the CDC-recommended lab sequence, a reactive antigen/antibody test is followed by a test that distinguishes HIV-1 from HIV-2 antibodies, and sometimes by a NAT. This is why a first positive result is called preliminary — no one gets a diagnosis from a single test. Source: CDC
Criminalization (HIV criminalization): Laws that make it a crime for a person who knows they have HIV to do certain things, such as have sex without telling a partner. As of 2023, 34 states had laws criminalizing HIV exposure, and many cover acts that cannot transmit HIV, like spitting or biting. Since 2014, at least 13 states have modernized or repealed these laws. Source: CDC

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Descovy (emtricitabine/tenofovir alafenamide (FTC/TAF)): A two-medicine combination pill containing emtricitabine and tenofovir alafenamide, FDA-approved on April 4, 2016. Because it is not a complete regimen on its own, it is taken with at least one other HIV medicine for treatment. For some people it is also used as daily PrEP. Source: NIH HIVinfo
Diagnosed vs Undiagnosed HIV (Knowledge of status): Not everyone living with HIV knows it yet. "Knowledge of status" is the share of people with HIV who have been tested and diagnosed, calculated by dividing people living with diagnosed HIV by total estimated HIV prevalence, diagnosed and undiagnosed. The EHE goal is 95 percent, up from 85.8 percent in 2017. Source: HIV.gov AHEAD
Disclosure: Choosing to tell someone that you are living with HIV. Your HIV status is confidential medical information, and sharing it with friends, family, or coworkers is your decision. It is important to tell sex partners and anyone you have shared needles with, and your provider or health department can notify partners for you without using your name. Source: HIV.gov
Dovato (dolutegravir/lamivudine (DTG/3TC)): A single-tablet, two-drug HIV treatment combining dolutegravir and lamivudine, FDA-approved on April 8, 2019. Federal guidelines recommend this two-drug combination as a first regimen for many people, with a few exceptions your care team checks for first. Source: NIH HIVinfo
DoxyPEP (Doxycycline post-exposure prophylaxis): Taking a 200 mg dose of the antibiotic doxycycline within 72 hours after oral, vaginal, or anal sex to lower the chance of getting a bacterial STI. CDC recommends discussing it with gay and bisexual men and transgender women who have had syphilis, chlamydia, or gonorrhea in the past year. It is offered as part of broader sexual health care. Source: CDC
Drug Resistance (Resistance): When a virus or other germ changes form and a medicine that used to work against it stops working as well. HIV drug resistance can lead to treatment no longer holding the virus down. Resistance testing helps your care team pick a regimen the virus cannot outmaneuver. Source: NIH Clinicalinfo HIV Glossary

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EHE (Ending the HIV Epidemic in the U.S.): Ending the HIV Epidemic in the U.S. is a federal initiative to sharply reduce new HIV transmissions by scaling up four strategies: diagnose, treat, prevent, and respond. It directs extra resources, expertise, and technology to 57 areas of the country where HIV transmission is most common, with a goal of at least 90 percent fewer new infections by 2030. Source: HIV.gov
EHE Jurisdictions (EHE priority jurisdictions): The 57 places the Ending the HIV Epidemic initiative focuses on first: 48 counties, Washington D.C., San Juan, Puerto Rico, and seven states with a large share of rural HIV diagnoses. They were chosen because, at the initiative's 2019 launch, they accounted for more than half of new HIV diagnoses nationally. Source: HIV.gov
ELISA (Enzyme-Linked Immunosorbent Assay; enzyme immunoassay): A lab test that looks for HIV antibodies in blood or oral fluid. The immune system makes these antibodies in response to HIV. A positive ELISA result always needs a second, follow-up test before anyone can be given a definite HIV diagnosis. Source: NIH Clinicalinfo
Elite Controller (Long-term non-progressor): A small number of people living with HIV stay healthy for many years without taking HIV medicine, because their immune systems hold the virus in check on their own. Researchers call them elite controllers or long-term non-progressors, and NIH studies them to learn how that natural control works. Source: NIH NIAID
Entry Inhibitor: A group of HIV medicines that stops HIV from getting into a CD4 cell in the first place. The group includes fusion inhibitors, CCR5 antagonists, and post-attachment inhibitors. These are usually used by people whose HIV has become resistant to other classes. Source: NIH Clinicalinfo
Enzyme Immunoassay (EIA) (EIA; ELISA): Another name for the ELISA — a lab test that looks for HIV antibodies in blood or oral fluid, made by the immune system in response to HIV. A reactive EIA is a screen, not a diagnosis: a second, different test must confirm it before anyone is told they have HIV. Source: NIH Clinicalinfo

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False Negative: A test result that says a condition is not there when it actually is. A false-negative HIV test tells someone they do not have HIV when they do. This is why testing again after the window period matters if there was a possible exposure. Source: NIH Clinicalinfo HIV Glossary
Fourth-Generation Test (4th-generation antigen/antibody immunoassay): The lab test CDC recommends starting HIV testing with. It detects HIV-1 and HIV-2 antibodies plus HIV-1 p24 antigen, so it can find HIV before antibodies appear — that is, during acute infection. If it is reactive, the lab runs a test that tells HIV-1 and HIV-2 antibodies apart, and sometimes a NAT. Source: CDC
Fusion Inhibitor: A class of HIV medicines that keeps HIV's outer envelope from merging with the membrane of a CD4 cell. Because that merging is how HIV gets inside, blocking it keeps the virus out of the cell. Source: NIH Clinicalinfo

G

Genotype Test (Genotypic antiretroviral resistance test (GART)): A resistance test that reads HIV's genes to spot mutations that make certain HIV medicines less effective. Results guide your care team in choosing or changing a regimen. A blood sample for genotype testing is usually drawn when you start care — and it should not delay starting treatment. Source: NIH Clinicalinfo HIV Glossary
Getting to Zero (Zero new infections, zero discrimination, zero AIDS-related deaths): A framing that came out of UNAIDS strategy and is now used by cities and states: zero new HIV infections, zero discrimination, and zero AIDS-related deaths. It pairs treatment and prevention goals with human rights goals — including repealing punitive laws and ending violence and stigma. Source: UNAIDS
Global Fund (The Global Fund to Fight AIDS, Tuberculosis and Malaria): A worldwide partnership that raises and invests more than US$4 billion a year to fight HIV, tuberculosis, and malaria in more than 100 of the hardest-hit countries. It brings together governments, civil society, communities, health workers, and private partners, and countries themselves decide how best to shape their response. Source: The Global Fund

H

Harm Reduction: A set of practical, respectful strategies for reducing the harms tied to drug use and other risks — without requiring anyone to stop first. Harm reduction accepts a person's own goals, treats them with dignity, and counts any step that reduces harm as progress. Abstinence is one possible goal on that continuum, not the price of entry. Source: SAMHSA
Hepatitis B (HBV) (Hepatitis B virus infection): A virus that affects the liver and can pass through blood, semen, or other body fluids during sex or through shared injection equipment. In people living with both HBV and HIV, hepatitis B tends to progress faster than in people with HBV alone. There is a vaccine, and treatment choices matter — some HIV medicines also treat HBV. Source: NIH Clinicalinfo HIV Glossary
Hepatitis C (HCV) (Hepatitis C virus infection): A virus affecting the liver that usually passes through blood, and rarely through other body fluids. In people living with both HCV and HIV, hepatitis C progresses faster than in people with HCV alone. Hepatitis C is now curable for most people with a course of direct-acting antiviral pills. Source: NIH Clinicalinfo HIV Glossary
HIPAA: The Health Insurance Portability and Accountability Act of 1996. Its Privacy Rule sets national standards protecting your identifiable health information, in any form, held by providers, health plans, and their partners. In practice, that means your HIV test results and care records cannot be shared without your permission, apart from a few narrow exceptions. Source: U.S. HHS
HIV (Human Immunodeficiency Virus): The virus that, without treatment, can lead to AIDS. HIV is a retrovirus with two types, HIV-1 and HIV-2. It passes through direct contact with certain body fluids, such as blood, semen, and vaginal fluid, or from a parent to a child during pregnancy, birth, or breastfeeding. Treatment keeps HIV under control. Source: NIH Clinicalinfo HIV Glossary
HIV Drug Resistance Test (Phenotype) (Phenotypic antiretroviral resistance test; phenotypic assay): A resistance test that grows a person's own HIV against different amounts of HIV medicines to see which ones still hold it back. Unlike a genotype test, which reads the virus's genes, a phenotype test measures behavior directly. It is mainly used when resistance is complicated, to help pick a regimen that will work. Source: NIH Clinicalinfo HIV Glossary
HIV RNA Test (NAT) (Nucleic acid test; NAAT; nucleic acid amplification test): A lab test that looks for HIV's genetic material — the virus itself — in blood, rather than looking for antibodies. It can tell whether a person has HIV and how much virus is in the blood (the viral load). A NAT detects HIV earliest, usually about 10 to 33 days after exposure. Source: NIH Clinicalinfo
HIV Test Positivity Rate (Percent positivity): A program measure: the share of HIV tests done that came back positive. CDC calculates it by dividing positive test events by all test events. Programs also track newly diagnosed positivity separately. A higher rate can mean testing is reaching the people who most need it. Source: CDC
HIV-1 vs HIV-2 (HIV type 1; HIV type 2): There are two types of HIV. HIV-1 causes most HIV worldwide, and in the U.S. "HIV" usually means HIV-1. HIV-2 is found mainly in West Africa and generally takes longer to progress. Both pass the same ways, and both are treatable — though some medicines work differently against HIV-2, so knowing the type matters. Source: NIH Clinicalinfo
Home HIV Test (HIV self-test; self-testing): A test you can take at home or anywhere private. The FDA-approved HIV self-test uses oral fluid and gives a result in about 20 minutes; home collection kits let you mail a fingerstick sample to a lab. Self-testing puts knowing your status on your own terms — and a positive result is followed up with a lab test. Source: CDC
HOPWA (Housing Opportunities for Persons With AIDS): Housing Opportunities for Persons With AIDS is the only federal program dedicated to the housing needs of people with HIV who have low incomes, and their families. HUD's Office of HIV/AIDS Housing runs it, and grantees work with nonprofits and housing agencies to provide housing plus supportive services. Source: HUD
Housing First: An approach that puts people directly into permanent housing without requiring them to complete services, get sober, or meet other conditions first. Support services are offered and readily available, but participation is voluntary, and a relapse does not cost someone their home. Case management continues to help people stay housed. Source: HUD
HRSA (Health Resources and Services Administration): The Health Resources and Services Administration is the main federal agency working to improve access to health care for people who are uninsured, isolated, or hit hardest by health problems. Through its HIV/AIDS Bureau, HRSA runs the Ryan White HIV/AIDS Program, the largest federal program focused only on HIV care. Source: NIH Clinicalinfo HIV Glossary

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Immune Reconstitution (Immune Reconstitution Inflammatory Syndrome (IRIS)): As HIV treatment works and the immune system starts recovering, it can sometimes react strongly to an infection already in the body. Doctors call this immune reconstitution inflammatory syndrome (IRIS). It can unmask an infection no one knew about, or flare one being treated. IRIS is manageable and does not mean treatment is failing. Source: NIH Clinicalinfo HIV Glossary
Incidence (New infections): The number of new cases of a condition that happen in a certain place over a certain period of time. HIV incidence means new HIV infections — which is different from new diagnoses, since someone can acquire HIV years before they are diagnosed. Source: NIH Clinicalinfo HIV Glossary
Integrase Inhibitor (Integrase strand transfer inhibitor (INSTI)): A class of HIV medicines that blocks integrase, an HIV enzyme. HIV uses integrase to insert its genetic material into the DNA of a CD4 cell; blocking it stops HIV from making copies of itself. Integrase inhibitors anchor most first-line regimens today because they work fast and are usually well tolerated. Source: NIH Clinicalinfo HIV Glossary

K

Kaposi Sarcoma (KS): A rare cancer of the cells lining lymph and blood vessels. It causes red or purple patches called lesions under the skin or in the mouth, nose, and throat, and sometimes in the digestive tract, liver, or lungs. It mainly affects people with weakened immune systems, and in people with HIV it is an AIDS-defining condition. Source: NIH Clinicalinfo

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Late Diagnosis: Finding out you have HIV after the virus has already done significant damage to the immune system — for example, being classified as stage 3 (AIDS) around the time of diagnosis. CDC surveillance records the stage of disease at diagnosis to track this. A late diagnosis is a reason to start treatment right away, not a reason for blame. Source: CDC
Linkage to Care: The step between an HIV diagnosis and actually getting into medical care. CDC measures it as having at least one CD4 or viral load test within one month of diagnosis — including tests done the same day. Fast linkage means faster treatment, and it is something clinics and navigators are responsible for making easy. Source: CDC
Linkage-to-Care Coordinator (Care navigator; linkage coordinator): A staff person whose job is to make sure someone who tests positive actually reaches HIV medical care, without falling through cracks. In programs like Oregon's Early Intervention Services and Outreach work, a full-time coordinator ties testing, prevention, and care together so referrals from the testing site are seamless. Source: HRSA TargetHIV
Long-Acting Injectable (LAI; long-acting ART): HIV medicine given as a shot rather than a daily pill, so it is taken far less often. FDA-approved long-acting options include injections for HIV treatment and for prevention. They are not the right fit for everyone, so it is a conversation to have with your care team. Source: NIH HIVinfo
Long-Term Survivor (Lifetime survivor): People who have lived with HIV for many years — often more than a decade, sometimes since before effective treatment arrived in 1996, and sometimes since birth (also called lifetime survivors or "dandelions"). Many carry health effects from years of virus and early harsh medicines. HIV Long-Term Survivors Awareness Day is June 5. Source: NIH HIVinfo

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Medicaid: The largest public health insurance program in the U.S., jointly funded by states and the federal government for people with low incomes. It is also the single biggest source of coverage for people with HIV, covering roughly 40 percent of nonelderly adults living with HIV. States run their own programs, so benefits and eligibility vary. Source: KFF
Molecular Surveillance (HIV cluster detection): A public health method that uses genetic sequences of HIV from people who are newly diagnosed to find clusters of connected transmissions. It helps health departments see where HIV is spreading quickly so they can direct prevention, testing, and care resources there. Community trust and data privacy are central concerns in how it is used. Source: UNAIDS/WHO
MPT (Multipurpose Prevention Technology): Multipurpose prevention technologies are products designed to meet more than one sexual and reproductive health need at once. Condoms are an example that already exists. Newer MPTs in development include rings, films, implants, gels, and the Dual Prevention Pill, which combines oral PrEP with birth control in one daily pill. Source: AVAC

N

New HIV Diagnoses (HIV diagnoses): The count of people newly diagnosed with HIV in a given year, at any stage of disease. CDC reports these by the date of diagnosis rather than the date the case was reported, through the National HIV Surveillance System, which collects data from all 50 states, D.C., and 7 territories. Source: CDC
NNRTI (Non-nucleoside reverse transcriptase inhibitor): A class of HIV medicines that attaches to reverse transcriptase and blocks it, stopping HIV from copying its genetic material. NNRTIs work on the same enzyme as NRTIs but in a different way, so the two classes are often used together in a regimen. Source: NIH Clinicalinfo
nPEP (Non-occupational post-exposure prophylaxis): Non-occupational post-exposure prophylaxis: PEP started after a possible HIV exposure outside of work, such as during sex or from sharing injection equipment. It is short-term medicine begun as soon as possible after the exposure to keep HIV from taking hold, and it is treated as urgent care. Source: NIH Clinicalinfo HIV Glossary
NRTI (Nucleoside reverse transcriptase inhibitor): A class of HIV medicines that blocks reverse transcriptase, an enzyme HIV needs to turn its RNA into DNA. Without that step, HIV cannot copy itself. NRTIs such as emtricitabine, lamivudine, and tenofovir form the backbone of most HIV regimens. Source: NIH Clinicalinfo

O

oPEP (Occupational post-exposure prophylaxis): Occupational post-exposure prophylaxis: PEP started as soon as possible after a possible workplace exposure to HIV, hepatitis B, or hepatitis C — for example, a needlestick injury in a health care setting. The goal is to keep an infection from taking hold. Source: NIH Clinicalinfo HIV Glossary
Opportunistic Infection (OI) (OI): An infection that shows up more often, or hits harder, in people whose immune systems are weakened — including people with untreated HIV or people on chemotherapy. HIV treatment that restores the immune system is the best protection, and most OIs can be prevented or treated. Source: NIH Clinicalinfo HIV Glossary

P

PEP (Post-exposure prophylaxis): Post-exposure prophylaxis is short-term medicine started as soon as possible after a possible exposure to HIV, hepatitis B, or hepatitis C, to lower the chance of infection taking hold. For HIV, PEP is an emergency measure — the sooner it starts, the better it works. Source: NIH Clinicalinfo HIV Glossary
PEPFAR (President's Emergency Plan for AIDS Relief): The U.S. President's Emergency Plan for AIDS Relief, the American government's global HIV program. Led through the Bureau of Global Health Security and Diplomacy, PEPFAR works in more than 50 countries to save lives, prevent new HIV infections, and move toward control of the HIV pandemic. Source: U.S. Department of State
Person-First Language (Person-centered language): Language that centers the person rather than a condition or status — "a person living with HIV" rather than "an HIV-infected person." UNAIDS guidance notes that language can carry stigma that affects whether people test, seek care, and stay in treatment. Some communities prefer identity-first language, so asking about local preference matters. Source: UNAIDS
PLHIV (People living with HIV): Short for people living with HIV. UNAIDS recommends this phrasing over labels like "HIV-infected," "AIDS patient," or "AIDS victim," because many people feel those terms reduce a whole person to a virus. "HIV-positive" is still used clinically to describe a test result, but not as someone's identity. Source: UNAIDS
Pneumocystis Pneumonia (PCP) (PJP; Pneumocystis jirovecii pneumonia): A lung infection caused by the fungus Pneumocystis jirovecii, with symptoms like a dry cough, fever, and shortness of breath. The fungus is common in the environment and harmless to people with healthy immune systems. In people with HIV, PCP is an AIDS-defining condition, and it can be both prevented and treated. Source: NIH Clinicalinfo
PrEP (Pre-exposure prophylaxis): Pre-exposure prophylaxis is HIV medicine taken by people who do not have HIV to prevent getting it. PrEP comes as pills and as long-acting shots, on a regular dosing schedule, and it works even better alongside condoms and other prevention tools. Source: NIH Clinicalinfo HIV Glossary
PrEP2Prevent (NCT05281393): An NIH-funded research study testing an online PrEP navigation and activation program for young men who have sex with men and young transgender and nonbinary people. It pairs a mobile health platform with a patient navigator, peer support, and goal setting to help people get on and stay on PrEP. Source: ClinicalTrials.gov
Prevalence: The number or share of people living with a particular condition in a population at a given time. HIV prevalence counts everyone living with HIV, whether they were diagnosed last month or twenty years ago. Source: NIH Clinicalinfo HIV Glossary
Protease Inhibitor (PI) (PI): A class of HIV medicines that blocks protease, an HIV enzyme. Without protease, newly made HIV stays immature and cannot go on to infect other CD4 cells. PIs are dependable options, often used when resistance or other health factors rule out other classes. Source: NIH Clinicalinfo
Provirus (Proviral DNA): The form HIV takes once it has slipped its genetic material into a cell's own DNA. After HIV enters a CD4 cell, its RNA is copied into DNA — the provirus — which is then inserted into the cell's DNA and passed along when that cell divides. This is a big part of why HIV is so hard to cure. Source: NIH Clinicalinfo

R

Rapid HIV Test (Point-of-care test): An HIV screening test that gives results in under 30 minutes, using blood from a finger stick or oral fluid. Most rapid tests look for HIV antibodies, and a rapid antigen/antibody version also exists. A positive rapid result is preliminary: it always needs a follow-up test to confirm a diagnosis. Source: NIH Clinicalinfo
Rapid Start (Rapid ART initiation; same-day start): Starting HIV treatment the same day as diagnosis, or very soon after. Federal guidelines recommend starting ART immediately, or as soon as possible, after diagnosis: it gets more people on treatment, shortens the time to an undetectable viral load, and improves how many people stay virally suppressed. Source: DHHS HIV Guidelines
Recency Testing (Recency assay; RITA): A surveillance tool that uses lab markers to estimate whether someone acquired HIV recently — usually within about the past year — or longer ago. Results are combined with viral load and other information in a recent infection testing algorithm. WHO and UNAIDS say these results are for public health planning, not for individual care, and are not given back to individuals. Source: UNAIDS/WHO
Reservoir (Latent HIV reservoir): Resting CD4 cells and other cells that carry HIV but are not actively making new virus. These latent reservoirs form in the earliest days of HIV and survive even when treatment drives the viral load to undetectable. Because ART cannot clear them, it cannot cure HIV — and shrinking them is a major focus of cure research. Source: NIH Clinicalinfo
Retention in Care: Staying connected to HIV care over time. CDC measures it as having at least two CD4 or viral load tests, at least three months apart, during a year. Life gets in the way for everyone, and clinics, case managers, and peer navigators exist to help you get back in care whenever you need to. Source: CDC
Ryan White Parts A/B/C/D/F (RWHAP Parts): The Ryan White program has five parts, each funding something different. Part A funds care in the cities and counties most affected by HIV. Part B funds states and territories, including ADAP. Part C funds outpatient care at community clinics. Part D funds care for women, infants, children, and youth. Part F funds provider training, innovation, dental care, and the Minority AIDS Initiative. Source: HRSA
Ryan White Program (Ryan White HIV/AIDS Program (RWHAP); CARE Act): The largest federally funded program providing HIV care and support to people with HIV who have low incomes or are uninsured or underinsured. HRSA administers it, and each year more than 600,000 people — over half of everyone diagnosed with HIV in the U.S. — get services through it, in all 50 states, D.C., and the territories. Source: HRSA

S

Same-Day Start (Same-day ART initiation): Beginning HIV treatment on the day of diagnosis. Federal guidelines support this to get more people on ART, shorten the time to viral suppression, and keep people engaged in care. Clinics make it work by pulling education, counseling, insurance help, labs, and a starter pack of medicine into one visit. Source: DHHS HIV Guidelines
Sero-prevalence (Seroprevalence): How common a condition is in a defined group of people at one point in time, measured through blood tests. For HIV, seroprevalence surveys estimate what share of a population has HIV antibodies. Public health programs use these estimates to understand where HIV is concentrated and where testing, prevention, and care should be strengthened. Source: NIH Clinicalinfo HIV Glossary
Seroconversion: The point when the body has made enough HIV antibodies for an antibody test to detect them, usually within a few weeks of acquiring HIV. At seroconversion, an HIV antibody test result changes from negative to positive. Source: NIH Clinicalinfo HIV Glossary
Serodifferent (Mixed-status couple; serodiscordant): A couple in which one partner is living with HIV and the other is not. Also called a mixed-status couple. When the partner living with HIV is on treatment with an undetectable viral load, HIV is not passed through sex — and the other partner may also choose PrEP. Source: NIH Clinicalinfo HIV Glossary
Serosorting: Choosing sex partners who have the same HIV status you do, or saving condomless sex for partners of the same status. It has real limits as a strategy: an HIV-negative person only knows their status as of their last test, so serosorting is often combined with — or replaced by — PrEP and treatment. Source: aidsmap
Sexual Health Clinic (STI clinic; STD clinic): A clinic that specializes in sexual health care — timely, confidential, and culturally sensitive. Services usually include STI and HIV testing and treatment, PrEP and nPEP, vaccinations, condoms, counseling, and partner services. Many offer walk-in, low-cost care and act as a safety net for people without insurance. Source: CDC
Single-Tablet Regimen (STR) (STR; fixed-dose combination (FDC)): A complete HIV regimen combined into one pill taken once a day. Fixed-dose combinations like this cut down how many pills a person takes, which can make treatment far easier to keep up with. Most regimens recommended for starting treatment today are one or two pills once daily. Source: NIH Clinicalinfo
Stigma (HIV-related stigma): Negative beliefs and attitudes attached to a condition or to the people living with it. Beliefs about HIV can lead to people living with HIV being judged, avoided, or mistreated — and that stigma harms health and well-being. Accurate information, like U=U, and person-first language help dismantle it. Source: NIH Clinicalinfo HIV Glossary
Suppressed / Virally Suppressed (Viral suppression; virologic control): When HIV treatment lowers the amount of virus in the blood to a very low level; CDC uses a viral load under 200 copies/mL. Being suppressed protects your immune system and means you will not pass HIV to sex partners. It does not mean HIV is cured — the virus is still there, so treatment continues. Source: NIH Clinicalinfo HIV Glossary
Syringe Services Program (SSP) (SSP; needle exchange): A community-based program that provides sterile syringes, safe disposal of used equipment, testing and vaccination for infectious diseases, and links to treatment for both infections and substance use. Nearly 30 years of research shows SSPs are safe, effective, and cost-saving; they are linked to about a 50 percent drop in new HIV and hepatitis C. Source: CDC

T

Test-and-Treat (Treat all): The approach of offering HIV treatment to everyone living with HIV, as soon after diagnosis as possible, rather than waiting for lab thresholds. WHO's "treat all" recommendation removed all eligibility limits on ART, because starting early keeps people healthier and reduces the chance of passing HIV to partners. Source: WHO
Treatment as Prevention (TasP) (TasP): Using HIV treatment itself as prevention. A person living with HIV who takes ART and keeps an undetectable viral load cannot pass HIV to sex partners. TasP also improves quality of life and lifespan, which is why global guidance recommends treatment for everyone living with HIV. Source: UNAIDS
Treatment Cascade (HIV care continuum; HIV continuum of care): A way of describing the steps of HIV care: getting diagnosed, finding the right care, starting ART, staying on treatment, and staying in care — with viral suppression as the goal. Programs also use it to see where people fall out of care so they can fix those gaps. Source: NIH Clinicalinfo HIV Glossary
Treatment Naive (ARV-naive): A person living with HIV who has never taken antiretroviral medicines. Someone can be treatment naive whether they were diagnosed yesterday or years ago. It carries no judgment — it is simply a starting point that tells your care team the virus has not been exposed to HIV drugs before, which widens the choice of first regimens. Source: NIH Clinicalinfo HIV Glossary
Truvada (emtricitabine/tenofovir disoproxil fumarate (FTC/TDF)): A combination pill containing emtricitabine and tenofovir disoproxil fumarate, FDA-approved on August 2, 2004. As HIV treatment it is taken alongside at least one other medicine, and it is also a long-standing daily PrEP option. Generic versions are available, which can make it a lower-cost choice. Source: NIH HIVinfo
Tuberculosis (TB): A bacterial infection that spreads through the air when a person with active TB coughs, sneezes, speaks, or sings. It usually affects the lungs but can reach the kidneys, spine, or brain. TB comes in two forms — latent TB and TB disease — and in people with HIV, TB disease is an AIDS-defining condition. Both forms are treatable. Source: NIH Clinicalinfo
Two-Drug Regimen (Dual therapy): An HIV treatment regimen built from two medicines instead of the traditional three. Dolutegravir plus lamivudine is the one two-drug combination federal guidelines recommend for starting treatment. It is not used during pregnancy, with hepatitis B coinfection, with a very high viral load, or before resistance and hepatitis B results are back. Source: DHHS HIV Guidelines

U

U=U (Undetectable = Untransmittable): Undetectable equals untransmittable. A person living with HIV who takes ART as prescribed and has an undetectable viral load cannot pass HIV to another person. U=U is a global campaign built on that evidence, and it exists to reduce stigma and support access to treatment and care. Source: UNAIDS
Undetectable Viral Load: When there is so little HIV in the blood that a viral load test cannot find it. A viral load is called durably undetectable once it stays undetectable for at least six months after the first undetectable result. Undetectable does not mean cured — HIV is still in the body, so treatment continues. Source: NIH Clinicalinfo HIV Glossary

V

Viral Load (HIV RNA level; VL): The amount of HIV in a sample of blood, reported as copies of HIV RNA per milliliter. A main goal of HIV treatment is to bring your viral load down to undetectable — too low for the test to find. Viral load tests also help diagnose recent HIV and guide treatment choices. Source: NIH Clinicalinfo HIV Glossary
Viral Rebound (Rebound): When someone on HIV treatment has a viral load that becomes detectable again after a stretch of being undetectable. Common causes include drug resistance or gaps in taking medicine. A rebound is information, not failure — your care team can adjust the regimen or add support. Source: NIH Clinicalinfo HIV Glossary

W

Window Period: The stretch of time between a possible HIV exposure and when a test can actually detect HIV. It varies by test: about 10 to 33 days for a nucleic acid test, 18 to 45 days for a lab antigen/antibody test, and 23 to 90 days for antibody tests. A negative result during this period may need repeating. Source: CDC