Noun
pre-exposure prophylaxis (uncountable)
(medicine) A form of prevention, usually medication, that is taken before exposure to a pathogen, preventing development of disease after such exposure.
Synonym: PrEP
(especially) A preventative medical regiment of HIV medicines used to protect against HIV seroconversion after an exposure.
Some doctors will prescribe pre-exposure prophylaxis to sexually active people to prevent them from getting HIV/AIDS.