A fuck that's only marginally better than a wank (ie. having sex with this chick will only be slightly better than masturbating to your best pornographic material).
Technically a term that only applies to 6's, but apply to all normal day women so you know there's nothing at stake.
A guy sees your run-of-the-mill hot chick and is not impressed.
Guy 1: She's a wank and a half, isn't she?
Guy 2: Totally.
A chick is a WAAH if she's only got her physical appearance and it's not even of supermodel quality.