A girl that is mixed with a lot of nationalities. She more than likely has everything a man could ever want. Short for Pretty Mixed Bitch.
Boy 1: Hey man you see that girl over there?
Boy 2: Yeah dude, the one with the big azz?
Boy 1: Hell Yeah, that is what you call a PMB.
Boy 2: A what?
Girl: A Pretty Mixed Bitch. (smacks ass)
Boy 1&2: DAMN!!!!