PEP is a month-long course of drugs that, if taken within 72 hours of the HIV virus entering the body, can prevent a person becoming infected with HIV. The PEP drugs are the same drugs that people who have the HIV virus use to reduce its impact on the body.
PEP is short for Post Exposure Prophylaxis.
Post = after
Exposure = a situation where HIV enters someone's body (eg: during unprotected sex or by sharing needles)
Prophylaxis = treatment for disease