Pool (cue sports)

Pool is a series of cue sports played on a billiard table. The table has six pockets along the rails, into which balls are shot. Of the many different pool games, the most popular include: eight-ball, blackball, nine-ball, ten-ball, seven-ball, straight pool, one-pocket, and bank pool. Eight-ball is the most frequently played discipline of pool, and it is often thought of as synonymous with "pool".

The generic term pocket billiards is sometimes also used, and favored by some pool-industry bodies, but is technically a broader classification, including games such as snooker, Russian pyramid, and kaisa, which are not referred to as pool games. There are also hybrid games combining aspects of both pool and carom billiards, such as American four-ball billiards, bottle pool, cowboy pool, and English billiards.

The etymology of "pool" is uncertain. The Oxford English Dictionary speculates that "pool" and other games with collective stakes is derived from the French poule (literally translated "hen"), in which the poule is the collected prize, originating from jeu de la poule, a game that is thought to have been played during the Middle Ages. Supposedly, participants would put an equal amount of money into a pot and throw stones at a live chicken, and the person who successfully hit the chicken first would win the pooled money. Alternatively the term could derive from the verb to pool in the sense of combining objects or stakes. The oldest use of the word "pool" to describe a billiards-like game was made in 1797 in a Virginia newspaper. The OED defines it as generally "any of various types of billiards for two or more players" but goes on to note that the first specific meaning of "a game in which each player uses a cue ball of a distinctive colour to pocket the balls of the other player(s) in a certain order, the winner taking all the stakes submitted at the start of the contest" is now obsolete, and its other specific definitions are all for games that originate in the United States. In the British Empire for most of the nineteenth through early twentieth century, pool referred specifically to the game of life pool.

Although skittle pool is played on a pocketless carom billiards table, the term pool later stuck to all new games of pocket billiards as the sport gained in popularity in the United States, and so outside the cue sports industry, which has long favored the more formal term pocket billiards, the common name for the sport has remained pool. The OxfordDictionaries.com definition no longer even provides the obsolete meaning found in the print edition, and refers only to the typical game "using two sets [each] of seven coloured and numbered balls ... with one black ball and a white cue ball" on a table with pockets.

With the exception of one-pocket, games typically called "pool" today are descended from two English games imported to the United States during the 19th century. The first was English billiards which became American four-ball billiards, essentially the same game but with an extra red object ball to increase scoring opportunities. It was the most popular billiards game in the mid-19th century until dethroned by the carom game straight rail. American four-ball tournaments tried switching to carom tables in the 1870s but this did not save it from being doomed to obscurity; the last professional tournament was held in 1876. Cowboy pool is a surviving member of this group of games.

The second and more influential game was pyramid pool. By 1850 a variant called fifteen-ball pool became popular. Both games were supplanted by continuous pool in 1888, the immediate forerunner of straight pool (1910). New games introduced at the turn of the 20th century include Kelly pool and eight-ball. The distinctive appearance of pool balls with their many colors and division between solid and striped balls came about by 1889. Prior to this, object balls were uniformly deep-red and differentiated only by numbers. English pyramid pool and life pool players were the first to adopt balls with different colors. The stripes were the last addition.

Pool is played on a six pocket table. Modern pool tables generally range in size from 3.5 by 7 feet (1.07 by 2.13 m), to 4.5 by 9 feet (1.37 by 2.74 m).

Under World Pool-Billiard Association (WPA) official equipment specifications, pool balls weigh from 5.5 to 6 oz (160 to 170 g) and have a diameter of 2.25 inches (57.15 mm), plus or minus 0.005 inches (0.127 mm). Modern coin-operated pool tables generally use one of three methods to distinguish and return the cue ball to the front of the table while the numbered balls return to an inaccessible receptacle until paid for again: the cue ball is larger and heavier than the other balls, or denser and heavier, or has a magnetic core.