Tennis balls are small, round objects used in the sport of tennis. They are typically bright yellow and made of a rubber core covered with a layer of felt. This design helps them bounce well on the court and makes them easy to see during a match. When players hit the ball with their tennis rackets, it travels quickly over the net, allowing for exciting rallies. Tennis balls are also used in practice sessions and can be found in various colors and types, including those designed for beginner players or professional tournaments.