Bowls is played on a level, grassed or synthetic playing surface and is surrounded by banks. The surface, called a "green", is divided into spaces called "rinks". On average, there are seven rinks to each green; so seven games can be played at any one time. To commence a game, a small spherical white ball, called a "jack", is delivered and placed on the centreline of the rink. Each player consecutively takes turns to deliver his or her bowls with the aim of finishing as close as possible to, or touching, the jack. After each player or team has delivered all their bowls, one point is scored for each bowl closer to the jack than the opponent's nearest bowl. This is termed the completion of an "end". Play resumes on the rink in the opposite direction until an agreed number of ends (usually 18 or 21) have been completed or an agreed number of points (21 or 25) have been reached. The game is played between two competitors (singles) or teams consisting of two (pairs), three (triples) or four players (fours). In singles and pairs each player uses four bowls, in triples three bowls, and in fours, two bowls.