The kind of fat that is on a girl around her mid waist which makes her not skinny but not fat. Its the kinda fat you want to fuck. Used like in the phrase "more cushion for the pushin' " without the girl being incredibly fat or unsexy
Also called FF for Fuck Fat.
Dan: you man, i want a girl, but all the hoes 'round here are all anerexic fuckers.
Zack: Dude, what 'bout Ellena?
Dan: Isn't she kinda heavy?
Zack: Naw man, i tapped that last week. Its All Sex Fat.
Dan: gotta love the FF.