Acronym, or code, for "Wants to Get Fucked".
A sarcastic code between guys to describe a woman who is dressed provocatively or projects sexuality. The woman is usually prematurely described as "wanting to get fucked". Usually used figuratively to say she's "turning you on", or she's "hot", not that she literally wants to get fucked there on the spot.
A related code is N.T.G.F. which stands for "needs to get fucked". A slightly stronger description.
I saw what she was wearing; she's W.T.G.F.
Did you see Keyra? She's W.T.G.F.-ing today.