Since the advent of the American bully, the term bully appears not to
refer to a group of breeds but to a breed that looks like the American
pitbull terrier. This breed is the American bully which is a poorly
conformed pitbull in looks and appearance that is too wide, too big and
just plain grossly exaggerated.
Some breeders are even rumored to be
secretly crossing in larger bully breeds in order to enhance the size of
the breed.
These poorly bred, badly conformed bully pitbulls from
unproven parents do not in any way represent the true form of the
American pitbull terrier. Bullies are not necessarily pitbulls and these
bully pitbulls are bred without regard to the preservation of the breed
standards of the pitbull.
The different breeders of this breed are all
driven by their own individual definition of what they think the bully
pitbull should be which essentially is: the more exaggerated or the
bigger the better.
http://www.aboutdogfacts.com/bully-pitbull/
Dog facts