Squash, sometimes called squash rackets, is a racket sport played by two (singles) or four players (doubles) in a four-walled court with a small, hollow, rubber ball. The players alternate striking the ball with their rackets, directing it onto the playable surfaces of the four walls of the court. The objective of the game is to hit the ball in such a way that the opponent is not able to play a valid return. There are about 20 million people who play squash regularly worldwide in over 185 countries.