There are three main breeds of pit bulls and several smaller offshoots. Like "terrier," "pit bull" is a descriptive term that encompasses many different breeds, coat types, colors and sizes. The three main ones are often confused, and it is best to differentiate them musculature and coat size when using general terms.
The three main types are the American Pitbull terrier, the American Staffordshire terrier and the Staffordshire bull terrier. The American Pitbull is roughly 30 to 60 pounds and has a variety of coat colors. Its head is proportionate to its body. In comparison, the American Staffordshire is a lot more muscular and bulky, and it takes on a square form. An American Staffordshire terrier usually weighs 60 to 90 pounds.
The Bull Terrier has a broad head and weighs in the same range as the American pitbull, but it retains some of the Staffordshire's bulk. All of the three breeds have short, smooth coats, but they can come in blue, red, tawny, brindle, black or brown.
Aside from the main breeds, there are terms like "gator pitbull," which refer to a specific breeding line that was bred for fighting and has since been bred out. When speaking about a dog, try to use its true breed name for clarification.