means: Anything but a face
Can both be used about a guy/girl who has a body which someone finds desirable, but a less attractive face.
This often occurs when beer goggles blind you and you wake up next to an abaf.
Markus: I scored with this hot fitness chick last night
Ronnie: O rly?
Markus: Yeah, but bcuz of my apparent alcohol intoxication the beer goggles tricked me
Ronnie: Oh, U sure been smokin dat crack, so was she an abaf?
Markus: 4 sho bro, ain't nothing to it but teh ugly.