The rattlesnake is a kind of snake, a reptile. About 50 kinds of rattlesnakes are known. They are a kind of pit viper. People of science call the two big groups of rattlesnakes (each called a genus) either Crotalus or Sistrurus. All of them have a poison bite, but some kinds are a much greater danger than others.
The name rattlesnake is used because they have a special tail with several parts on the end that can make a loud bzzzz sound, or rattle.