The friend who will stay by your side when you go out and/or dance with you while clubbing in order to keep the ugly/creepy/scary guys at bay. Unlike a Wing Man, this is not the girl who occupies the hot guy's ugly friend. Unlike women, guys have no problem ditching their friends for the hook-up (they just say, "peace out, man, I got to go tap that" and the discussion is closed). Wing Women are usually hot or at least cute so that they are easy to pass off if there happens to be a not so ugly/creepy/scary guy with whom the other woman would like to hook up. The Wing Woman position may be held simultaneously within a pair or group of women.
Good thing Evelyn was my Wing Woman or that creepy guy would have been grinding me on the dance floor.