Tennis is a sport played between either two players ("Singles") or two teams of two players ("doubles"). Players use a stringed racquet to strike a hollow rubber ball covered with felt over a net into the opponent's court. In some places tennis is still called lawn tennis to distinguish it from real tennis (also known as royal tennis or court tennis), an older form of the game that originated in France in the Middle Ages and is played indoors on a very different court. Originating in England in the late 19th century, lawn tennis spread first throughout the English-speaking world, particularly among the upper classes. Along with its millions of players, millions of people follow tennis as a spectator sport, especially the four Grand Slam tournaments.
Tennis is played on a rectangular, flat surface, usually grass, clay, or a hardcourt of concrete and/or asphalt. The court is 78 feet (23.77 m) long, and its width is 27 feet (8.23 m) for singles matches and 36 feet (10.97 m) for doubles matches. The net is 3 feet 6 inches (1.07 m) high at the posts, and 3 feet (914 mm) high in the center.
Types of Courts
There are three main types of courts. Depending on the materials used for the court surfaces, each surface provides a difference in the speed and bounce of the ball, which in turn can affect the level of play of the individual players.

The three most common types of courts are:
Clay court
Grass court
Hardcourt
Some players are more successful on certain surfaces and become known as, for instance, "Clay-court specialists".
Hardcourt encompasses many different surfaces ranging from old-fashioned concrete courts, to coated asphalt, to wooden gymnasium surfaces, to artificial grass similar to AstroTurf.
Clay courts are considered "slow", meaning that balls first lose speed as they hit the court and then bounce relatively high, making it more difficult for a player to hit an unreturnable shot, called a winner. On clay courts, line calls are easily reviewable because the ball leaves a visible mark.
Hardcourts and grass are "fast" surfaces, where fast, low bounces keep rallies short and where hard-serving and hard-hitting players have an advantage. Grass courts add an additional variable, with bounces depending on how healthy the grass is and how recently it has been mown.