Tennis is a game played between two players (singles) or between two teams of two players (doubles). Each player uses a strung racquet to strike a hollow rubber ball covered with felt (most of the time yellow, but can be any colour or even two-tone) over a net into the opponent's court.
There are four main types of courts depending on the materials used for the court surface: clay courts, hard courts, grass courts and indoor courts (carpet, rubber or wood). Each playing surface has its own characteristics which affect the playing style of the game.
Tennis is an Olympic sport and is played at all levels of society at all ages. The sport can be played by anyone who can hold a racquet, including people in wheelchairs. Along with its millions of players, millions of people worldwide follow tennis as a spectator sport, especially the four Grand Slam tournaments : Australian Open, French Open, Wimbledon, and the U.S. Open.