Unprotected sex

Unprotected sex refers to any act of sexual intercourse in which the participants use no form of barrier contraception.

Sexually transmitted infections
Specifically, unprotected sex usually refers to sexual activity in which the participants use no form of protection from sexually transmitted infections. It can thus be contrasted with "safe sex".

Advocates of the practice believe that sustained direct friction between skin and mucous membranes, and commingling of fluids, results in increased stimulation, fuller intimacy, and more powerful orgasms for all participants.

Birth control
Less commonly, unprotected sex is used to refer to sexual intercourse without the use of any form of contraception. The two meanings are different because there are forms of birth control that do not involve barrier protection such as hormonal contraception. This meaning is commonly used in discussions of fertility awareness, where couples avoiding pregnancy can identify infertile portions of the menstrual cycle where unprotected sex carries a very low risk of pregnancy.