Short for breakdancing girl. b-boy is the male version.

break-girl, the female version of b-boy. aka. a female breaker (a 'break-dancer' WITH style)

hip hop head in female version.

A B-girl is another word for calling a person a bitch. Although, that person could not always be a bitch, so they aren't actually a bitch. The person does, however, act bitchy on the occasion so they are a B-girl. The word is meant to be less harsh. There is no change in the word B-girl for males. If a male is being a bitch, then he too is a b-girl.