### Instruction: How many types of serves exist in tennis?
### Input: A serve (or, more formally, a service) in tennis is a shot to begin the point. The most common serve is used is an overhead serve. It is initiated by tossing the ball into the air over the server's head and hitting it when the arm is fully stretched out (usually near the apex of its trajectory) into the diagonally opposite service box without touching the net. The server may employ different types of serve: a flat, a top-spin, an American twist (or kick), or a slice serve. A severely sliced serve is sometimes called a sidespin. Some servers are content to use the serve simply to initiate the point; advanced players often try to hit a winning shot with their serve. A winning serve that is not touched by the opponent is called an ace.
### Response: There are different serve types in tennis. Overhead serve, flat serve, top-spin serve, kick serve and slice serve are some of the serve types.