HIV Terms and Definitions

What to know

These are some of the terms currently used by CDC's Division of HIV Prevention. This list of terms and their definitions may change over time.

Common terms and definitions

AIDS: Acronym for acquired immunodeficiency syndrome. AIDS is the most advanced stage of HIV.

Antibodies: Produced by your immune system when you're exposed to viruses like HIV.

Antibody test: An HIV test that looks for HIV antibodies in your blood or oral fluid.

Antigens: Foreign substances that cause your immune system to activate.

Antigen/antibody test: An HIV test thatlooks for both HIV antibodies and antigens.

ART: Acronym for antiretroviral therapy. ART is medicine used to treat HIV.

CD4 count: The number of CD4 cells you have in your blood. CD4 cells help your body fight infections.

Cisgender person: A person whose sex assigned at birth is the same as their gender identity or expression.

Diagnoses: The number of people who received an HIV diagnosis during a given year.

HIV: Acronym for human immunodeficiency virus. HIV is a virus that attacks the body's immune system.

HIV superinfection: When a person with HIV also gets another type, or strain, of the HIV virus.

Health equity: When everyone has a fair and just opportunity to attain their highest level of health.

Health disparities: Differences in health outcomes between populations disadvantaged by social, economic, or environmental factors.

Incidence: The estimated number of new HIV infections during a given year.

Mucous membrane: Body tissues found inside the rectum, vagina, penis, and mouth.

NAT: Acronym for nucleic acid test. A NAT is an HIV test that looks for the actual virus in the blood.

Transgender man: A person assigned female at birth who identifies as male.

Transgender person: A person whose gender identity or expression is different from their sex assigned at birth.

Transgender woman: A person assigned male at birth who identifies as female.

Viral load: The amount of HIV in the blood.

Viral load test: A test that can tell if a person has HIV or how much virus is present in the blood.

PEP: Acronym for post-exposure prophylaxis. PEP is medicine to prevent HIV after a possible exposure.

PrEP: Acronym for pre-exposure prophylaxis. PrEP is medicine that can reduce the chance of getting HIV.

Undetectable viral load: When the amount of HIV in the blood is so low that a test can't detect it.

Viral suppression: Having less than 200 copies of HIV per milliliter of blood.

Window period: The time between HIV exposure and when a test can detect HIV in your body.