Tennis, game played with a racket and a ball by two (as in singles) or four (as in doubles) competitors, on a rectangular court with a net strung between the mid-points of the longer sides of the court. Tennis may be played indoors or outdoors. The game ranks as one of the most popular spectator and participation sports in the world, with fans and competitors in more than 100 countries. Originally called “lawn tennis” to distinguish it from the sport of real tennis, from which it was derived, the game is now commonly known as tennis and is played on various surfaces other than on grass.

The court is marked with white lines to indicate its dimensions and service areas. The court is 23.8 m (78 ft) long, divided into two equal sides by a net standing 0.9 m (3 ft) high at the centre of the court. For singles, the court is 8.2 m (27 ft) wide. For doubles, the addition of margins 1.4 m (4y ft) wide along the two longer sides increases the width to 11 m (36 ft). Courts may be of grass, clay, asphalt, concrete, wood, artificial grass, or other synthetic materials.

A tennis ball is hollow and composed of inflated rubber covered with a fabric made of wool and artificial fibres. It is between 6 and 7 cm (2y and 2? in) in diameter and weighs between 57 and 58 g (2 and 2w oz). Yellow and white balls are used in tournament competition and are the most common colours, although balls of other colours are manufactured.