Anonymous sex is a form of one-night stand or casual sex between people who have very little or no history with each other, often engaging in sexual activity on the same day of their meeting and usually never seeing each other again afterwards. The term Cruising is used to refer to looking for anonymous sex, usually in specific places where such activity is commonplace. The internet is also a primary vehicle for people setting up anonymous sex. Anonymous sex can also take the form of prostitution, involving exchanges of money or drugs (particularly crack cocaine) for sex.

Some people engage in anonymous sex because of a perceived thrill of the act.