Coitus interruptus: A method of contraception, also called withdrawal, in which the man withdraws his penis from the vagina before ejaculation. Fertilization is prevented because the sperm do not enter the vagina.
The effectiveness of this maneuver depends on the man's ability to withdraw before the ejaculation of any sperm.
Withdrawal does not provide protection from sexually transmitted diseases (STDs) such as HIV. Infectious diseases can be transmitted by direct contact with surface lesions and by pre-ejaculatory fluid.