Squash is an indoor racquet sport that was formerly called "Squash racquets," a reference to the "squashable" soft ball used in the game (compared with the harder ball used in its parent game Racquets (or rackets; see below). The game is played by two players (or four players for doubles) with 'standard' rackets in a four-walled court with a small, hollow rubber ball.
Squash historians assert that the game originated in the 19th century at Harrow School, in London, England, as a derivative of the game of Rackets. Students at the school who were waiting to use the rackets court supposedly began hitting a softer rubber ball against the walls of the buildings with their rackets, and from this the game was ultimately created. The first recorded construction of purpose-built squash courts was at Harrow in the 1860s. It is possible that earlier squash courts were created at Harrow by sub-dividing a rackets court, which is almost exactly the size of three Squash courts (presumably to allow more players on the courts at the same time).
The game generally remained the preserve of the schools and universities until the early part of the 20th century, by which time it was becoming popular in the private clubs (such as the Royal Automobile Club in London) and with officers in the British armed forces.
The United States of America became the first nation to form a dedicated association and codify its game in 1907 (see Hardball squash). In the same year, the (British) Tennis and Rackets Association formed a squash rackets sub-committee to administer the game, which became progressively codified during the 1920s. Subsequently, the (British) Squash Rackets Association was formed and took over administration of the game in 1928. The game is now administered by the WSF (World Squash Federation). The men's professional game is managed by the PSA (Professional Squash Association) and the women's by WISPA (Women's International Squash Players Association).
Squash continued almost exclusively as the game of the upper-middle and upper classes until around the 1950s, when commercial operators began building public courts. The game boomed in popularity, with participation peaking around the early 1980s. Despite a downturn in player numbers, the game remains popular in many places, especially Australia, northwestern Europe, North America and Asia (primarily the south and southeastern regions thereof).
At the elite level, the game was strictly divided between amateur players (usually 'gentlemen' and 'ladies') and professional players, who were often coaches employed by the exclusive clubs. This division started to break down with the growth of the commercial side of the game in the 1960s, with the women's game becoming 'open' in 1973 and the men's game following suit in 1980.
The American style of doubles squash, which differs from the English style in its use of a hard ball and a slightly larger court, originated accidentally at a Philadelphia squash club in the 60s. The construction of a singles court facility at the club left an awkward space that was too small for 2 singles courts, and a local pro remarked that it would be the perfect size for a doubles court and created the rules of the new game on the spot. Since the invention of American doubles, the court-size has increased slightly, but the 'hard-ball' is still used even though is has almost completely disappeared from singles squash.