Applied by a guy when a girl is hot
, or to draw attention to the hotness of a girl.
Comes from the chorus of the song 'Get Low' by L'il Jon (3, 6, 9, damn she fine)
Jack: Hey Sam, look at that girl over there.
Jack 3, 6, 9
Sam: Damn she fine!!
Greg: Yo man, she a 3, 6, 9!