Virginity

In theory, virginity is a simple idea. Virginity is the state of not having had sex; a virgin is someone who hasn't had sex. But what counts as "having sex"--is it oral sex? vaginal sex? anal sex? Most people define it as not having had penis-vagina sex, though this definition doesn't work for everyone--a gay man, for example, is probably never going to have penis-vagina sex.