HIV Prevention Glossary
Every PrEP and HIV-prevention term, in clear language — PrEP, PEP, U=U, TDF, TAF, MSM, Doxy-PEP and more. Tap any term across the site to jump straight here.
PrEP Pre-exposure prophylaxis
Medicine an HIV-negative person takes to prevent getting HIV — a daily pill (Truvada/Descovy), a 2-monthly injection (Apretude), a twice-yearly injection (lenacapavir), or on-demand for anal sex. Highly effective when taken as prescribed.
PEP Post-exposure prophylaxis
Emergency HIV medicine started within 72 hours after a possible exposure and taken for 28 days. The sooner it starts, the better it works — it is not a substitute for ongoing PrEP.
HIV Human immunodeficiency virus
The virus that, untreated, damages the immune system. With modern treatment, HIV is controlled and untransmittable (see U=U).
ART Antiretroviral therapy
The combination of medicines a person living with HIV takes to suppress the virus. Effective ART leads to an undetectable viral load.
U=U Undetectable = Untransmittable
A person with HIV who takes treatment and stays undetectable cannot pass HIV on through sex — a cornerstone of modern prevention.
Viral load Amount of HIV in the blood
A measure of how much HIV is in the blood. Effective treatment lowers it to undetectable levels.
Undetectable Very low viral load
When treatment suppresses HIV so much that standard tests can't detect it. Undetectable means untransmittable (U=U).
Window period Time before a test is accurate
The gap between exposure and when an HIV test is reliable. PrEP needs a confirmed-negative test before starting.
Seroconversion Becoming HIV-positive
The period when a newly acquired HIV infection becomes detectable, sometimes with flu-like symptoms.
Serodifferent couple One partner has HIV, one doesn't
Also “serodiscordant” or “mixed-status.” With U=U and/or PrEP, these couples can have sex without passing on HIV.
MSM Men who have sex with men
A public-health term for men who have sex with men, however they identify. Some PrEP evidence (e.g. 2-1-1) is specific to this group.
Cisgender Gender matches birth-assigned sex
Describes someone whose gender identity matches the sex assigned at birth (e.g. “cisgender women”).
Transgender Gender differs from birth-assigned sex
Describes someone whose gender identity differs from their birth-assigned sex. PrEP works alongside gender-affirming hormones.
TDF Tenofovir disoproxil fumarate
The tenofovir form in Truvada — very effective and cheap as a generic, but needs kidney and bone monitoring.
TAF Tenofovir alafenamide
The newer tenofovir form in Descovy — gentler on kidneys and bones, but with modest weight/lipid changes and not approved for vaginal sex.
FTC Emtricitabine
The second active ingredient paired with tenofovir (TDF or TAF) in Truvada and Descovy.
CAB Cabotegravir
The long-acting integrase inhibitor in Apretude, given as an injection every 2 months.
Lenacapavir Yeztugo — twice-yearly PrEP
A capsid inhibitor injected just twice a year. FDA-approved in 2025; near-complete protection in trials, including cisgender women.
INSTI Integrase strand transfer inhibitor
A class of HIV medicine that blocks the integrase enzyme. Cabotegravir (Apretude) is an INSTI.
NRTI Nucleoside reverse transcriptase inhibitor
The drug class that includes tenofovir (TDF/TAF) and emtricitabine (FTC) — the backbone of oral PrEP.
2-1-1 / on-demand Event-driven PrEP
Taking Truvada around sex: 2 pills 2–24 h before, 1 at 24 h, 1 at 48 h. WHO-recommended for anal sex in MSM; not for vaginal sex and not FDA-approved.
Doxy-PEP Doxycycline post-exposure prophylaxis
A single 200 mg dose of doxycycline after condomless sex to cut bacterial STIs (chlamydia, syphilis). PrEP covers HIV only.
STI Sexually transmitted infection
Infections passed through sex (chlamydia, gonorrhoea, syphilis, etc.). PrEP does not protect against STIs — add testing, condoms and Doxy-PEP.
eGFR Estimated kidney function
A blood test of kidney function, checked before and during TDF-based PrEP. A falling eGFR may prompt a switch to Descovy or an injectable.
DEXA Bone-density scan
A scan measuring bone mineral density, considered for people on TDF with fracture-risk factors.
Adherence Taking PrEP as prescribed
How consistently PrEP is taken. High adherence = high protection; injectables remove the daily-pill challenge.
Grace window Injection timing leeway
The ±7-day window around an Apretude injection's due date. More than 7 days late risks losing protection.
Oral bridging Covering a gap with pills
Temporarily using daily oral PrEP to stay protected if an injection will be late, or during initiation.
Front-hole Inclusive anatomy term
An inclusive term some trans and non-binary people use for the vagina. PrEP timing for this tissue follows vaginal-sex guidance.
Receptive / insertive Sexual role
“Receptive” (bottom) and “insertive” (top) describe roles in sex; receptive exposure generally carries higher HIV risk.
Ready, Set, PrEP US free-PrEP program
A US national program providing PrEP medication at no cost to eligible uninsured people.
Dapivirine ring Monthly vaginal ring
A soft silicone ring worn in the vagina and replaced monthly. WHO-recommended extra option for cisgender women where approved; not FDA-approved.
Prophylaxis Prevention
Medicine or action taken to prevent disease — the “P” in PrEP and PEP.
Put the terms into action
Now that the jargon makes sense, see which PrEP fits you — or how to start.
🔬 Sources & review
Definitions written to U.S. CDC and WHO HIV-prevention guidance, USPSTF PrEP recommendations, and FDA labelling for Truvada, Descovy, Apretude and Yeztugo (lenacapavir).
✔ Last medically reviewed: 7 August 2026 · Prepmedication.com Medical Review Team · How we review →
Medical disclaimer. This glossary is general information, not a diagnosis or prescription. Terms and guidance vary by country and change over time — confirm your plan with a qualified clinician. If you may have been exposed to HIV in the last 72 hours, see PEP now.
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