n. Relatively small tits on a girl. It derivates from the term "struggling Bs." If a girl's tits are not quite B cup, but larger than your usual A cup, they could be considered struggling Bs. Also, "B" can be a short moniker for a black person. Therefore, struggling Bs can be called slaves.
Bro 1: Damn that girl has some tiny boobs.
Bro 2: Yeah, but I've seen smaller.
Bro 1: Yeah, I guess you're right, those are some slaves for sure.
Bro 2: For sure bro.