Tennis is a sport played between two players (singles) or between two teams of two players each (doubles). Each player uses a strung racquet to strike a hollow rubber ball covered with felt (most of the time Optic Yellow,[1] but can be any color or even two-tone) over a net into the opponent's court.

The modern game of tennis originated in the United Kingdom in the late 19th century as "lawn tennis" and had heavy connections to the ancient game of real tennis. After its creation, tennis spread throughout the upper-class English-speaking population before spreading around the world. 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 racket, including people in wheelchairs. In the United States, there is a collegiate circuit organized by the National Collegiate Athletics Association.

Except for the adoption of the tiebreaker in the 1970s, the rules of tennis have changed very little since the 1890s. A recent addition to professional tennis has been the adoption of "instant replay" technology coupled with a point challenge system, which allows a player to challenge the official call of a point.

Along with its millions of players, millions of people worldwide follow tennis as a spectator sport, especially the four Grand Slam tournaments (sometimes referred to as the "majors"): the Australian Open, the French Open, Wimbledon, and the US Open.