A gator is an alligator: the large reptile of the southern United States, especially Florida and Louisiana, with a wide snout. Gator is the short, spoken form. People say it in casual American English; you would not put it in a science test. Though actually, a gator is not the same animal as a crocodile. Alligators have a broader snout and live mostly in fresh water; crocodiles are a different family. In sport, the Florida Gators are a well-known university team — that nickname comes from the animal, and a sports drink later borrowed the sound. Don’t use gator for every big reptile in a picture, and don’t use it when you mean the other animal.