It is used sociologically in this context too. For example see:

http://links.jstor.org/sici?sici=0891-2432%28200206%2916%3A3%3C345%3AGATMAE%3E2.0.CO%3B2-H&size=LARGE&origin=JSTOR-enlargePage

Don’t forget that the word virgin is used in other contexts besides a sexual context and nonvirgin would be approriate in other contexts also. For instance, virgin and nonvirgin are used when describing such things as oils, cartridges and feedstocks:

http://www.google.co.uk/search?hl=en&q=nonvirgin+definition&btnG=Search&meta=

“Unchaste” would be one opposite word, but it sounds very old-fashioned. There was a time when “new bride” would have been used, coyly and rather indirectly, to convey the same meaning, but it doesn’t work anymore.

“Experienced” is useless, since one can be quite sexually experienced without engaging in penile-vaginal intercourse.

The problem, in our time, is that an unmarried female’s virginity was once closely connected to her worth; it was a concept closely connected to the totality of her being. This is no longer true.

We would want a word that more objectively and forthrightly conveys the sense that she had something that she no longer has.

I would suggest: “dehymenized.” But the presence or absence of a hymen is not a reliable indicator of virginity.

According to the Wikipedia artice, “hymen” there is an English translation of a French word used in translations of the works of the Marquis de Sade: depucelate. It is derived from the French verb, dépuceler. “Pucelle” is French for “virgin.”

So the opposite of “virgin” would be “depucelated” or “one who has been depucelated.”

I guess nymphomaniac and s l u t would fit that definition.

But if you simply mean a person her has had sex, as opposed to one who has not, non-virgin, as others have stated, seems to be right or the current popular phrase, already mentioned also, sexually active.

The closest thing that I can think of for someone who is depicted as having sex is “prostitute”. Although I think prostitute can be an umbrella term for things outside of sex.