(A) The large posterior (Ass) of a women (commonly of African Decent) that tends to move in a rocking motion due to size and shape.
(B) A women (commonly of African Decent) with a generous to large posterior (Ass) that is so awkward in shape and size to the rest of her body that it causes it to swing from side to side in a rocking motion.
(A) Damn, yo check that shit out. Shorty over there. Yo son she's got a heavy ass rocker
(B) Yo, she keeps walking like that she's gonna have my babies. Yo that chick is a rocker, look at em ass n hips move.