Friend of a friend. Like an acquaintance but with a little more familiarity, because odds are you've heard of them and they've heard of you and/or you've seen each other around the same crowds. Not quite a bff or a homeslice yet, because you haven't interacted with them enough to get those bonds yet.
Text1: So who's throwing the party?
Text2: A fof, she seems legit at the parties I've seen her at.