An individual who is not currently fat, but likely will be in the future, particularly after they age, bear (a) child(ren) or stop working out 3 times a day and start eating because they get married and thus tie their man down.
Often prefat is used as a derogatory comment, and with consideration not just of one's physical appearance but also their personality.
That whore at work may look decent now but she's prefat. Giver her 3 years, will be round as a ball.
Christy better be careful; I heard her say she want's a big family but you know she prefat. Those pounds aren't coming off after she pops a kid.
A overly possessive girl that seeks (or hunts) a guy (or prey) and gets pregnant from him just so she can use it as an excuse to stay with (or keep) him forever. Sometimes, the target male doesn't necessarily have to be the child's father.
Bob: Man, Hilary is so hot and awesome and I think she likes me, I'm totally going for it.
David: Dude, you gotta be careful around her, she's a total pregator.