Pit bull is an umbrella term for several types of dog believed to have descended from bull and terriers. In the United States, the term is usually considered to include the American Pit Bull Terrier, American Staffordshire Terrier, American Bully, Staffordshire Bull Terrier, and sometimes the American Bulldog, along with any crossbred dog that shares certain physical characteristics with these breeds. In other countries, including the United Kingdom, the term is used as an abbreviation of the American Pit Bull Terrier breed specifically, while the Staffordshire Bull Terrier is not considered a pit bull. Most pit bull-type dogs descend from the British bull and terrier, a 19th-century dog-fighting type developed from crosses between the Old English Bulldog and the Old English Terrier.

The American Pit Bull Terrier (APBT) is a dog breed recognized by the United Kennel Club (UKC) and the American Dog Breeders Association (ADBA), but not the American Kennel Club (AKC). It is a medium-sized, short-haired dog, of a solid build, whose early ancestors came from England. When compared with the English Staffordshire Bull Terrier, the American Pit Bull Terrier is larger by margins of 6–8 inches (15–20 cm) in height and 25–35 pounds (11–16 kg) in weight. The American Pit Bull Terrier varies in size: males are normally about 18–21 inches (45–53 cm) in height and around 35–60 pounds (15–27 kg) in weight, while females are normally around 17–20 inches (43–50 cm) in height and 30–50 pounds (13–22 kg) in weight.