APA Dictionary of Psychology

the use of a short course of antiretroviral medication taken after a potential exposure to human immunodeficiency virus (HIV) to reduce the risk of infection in a person without HIV. PEP should be started as soon as possible following possible exposure, at least within 72 hours, and is typically taken for 28 days. PEP is used as an emergency response following a single or unexpected exposure (i.e., unprotected sex, needle-stick injury, sharing drug injection equipment), and is not meant to replace regular prevention methods such as pre-exposure prophylaxis (PrEP).