Three-cushion

Three-cushion billiards (sometimes called three-cushion carom,three-cushion, three-cushions, three-rail, rails and the angle game, and often spelled with "3" instead of "three") is a popular form of carom billiards.

The object of the game is to carom the cue ball off both object balls and contact the rail cushions at least three times before the last object ball. A point is scored for each successful carom. In most shots the cue ball hits the object balls one time each, although hitting them any number of times is allowed as long as both are hit. The contacts between the cue ball and the cushions may happen before and/or after hitting the first object ball. The cue ball does not have to contact three different cushions as long as they have been in contact at least three times in total. Each player has his own cue ball. In modern Three Cushion Carambole are the neutral ball red, and the cue balls white and yellow. The introduction of the yellow ball (instead of two white ones) has not changed any rules, each player have always used a cue ball of his/her own. Earlier was there smaller markings on the white balls, in order to separate them from each other. The yellow ball just makes it easier for spectators to follow the game.

Three-cushion dates to the 1870s, and while the origin of the game is not entirely known, it evolved from cushion caroms, which in turn developed from straight rail billiards for the same reason that balkline also arose from straight rail. Such new developments made the game more challenging, less repetitive, and more interesting for spectators as well as players, by thwarting the ability of highly skilled players to rack up point after point at will by relying on nurse shots.

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Wikipedia