Pit Bull is reference to a type of dog usually including American pit bull terriers, American Staffordshire terriers or Staffordshire terriers, American Bully and crosses between them. Originally bred from terrier and bulldog breeds. I'm sure there's a lot more to it than my brief layman explanation, but even non-experts such as myself are able to identify some types of dogs from others by physical characteristics.

This gorgeous animal would fit the term Pit Bull.



And this guy would be a Pug.



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My guess is that there aren't a lot children being mauled by Pugs misidentified as Pit Bulls.