Damn you, Andy. I was looking up American Bulldogs and came across this picture:

The dog looks remarkably like Zach, the boxer I briefly adopted in 2007 who almost killed my dog Bandit and about whom I still feel very guilty and sad.
Be that as it may, here's is what Wikipedia says on the subject:
"Pit Bull is a term commonly used to describe several breeds of dog in the Molosser family that are commonly used for dog fighting. The breeds most often placed in this category are the American Pit Bull Terrier, American Staffordshire Terrier, and Staffordshire Bull Terrier.
"In the media the term is vague and may include other breeds with similar physical characteristics, such as the Perro de Presa Canario, Cane Corso, Dogo Argentino, Alano Espanol, Japanese Tosa, Dogue de Bordeaux, Cordoba Fighting Dog, Alapaha Blue Blood Bulldog, American Bulldog, Boxer, Valley Bulldog, Olde English Bulldogge, Renascence Bulldogge, and Banter Bulldogge. These breeds are rarely listed by name in breed-specific legislation, but they are sometimes included when the term is defined broadly and based on physical appearance."