A virgin is someone who has never had sex. After you have sex, you've lost your virginity. We can also say an unharvested forest is a virgin forest.
Virgins haven't had sex yet. But this word is also used in a non-sexual sense to describe something that remains pristine, untouched, or uninitiated. A virgin resource hasn't been used yet. If you've never given a speech, someone might call you a "public speaking virgin." So virgin always means inexperienced or unused, whether you're talking about sex or something else.