The Britannica does a fair job at identifying what a pitbull is. That they are decedents of a bulldog and terrier and were bred for hunting, capturing and restraining semi-feral livestock. The issue here is that unlike other definitions of the breed is that they do not have any sources for the statements that are within the definition by the Britannica, this does not work very well in a modern world of information.
(Add images of bull terrier and bulldog for visual reference)
Issues with the definition presented by the Britannica
Pibbles