1. A geometric form, usually aluminum, wooden or plastic, used to assist in setting up balls in games like eight-ball, nine-ball, and snooker. The rack allows for more consistently tight grouping of balls, which is necessary for a successful breakshot. In most games a triangle-shaped rack capable of holding fifteen balls can be employed, even if the game calls for racking less than a full ball set, such as in the game of nine-ball. For further information, see the Rack (billiards) main article.
2. Used to refer to a racked group of balls before they have been broken.
3. In some games, refers to a single frame.
4. Colloquial shorthand for "a set of balls".
5. Short for cuerack, wall rack or scoring rack when such abbreviation would not be ambiguous.
The act of setting up the balls for a breakshot. In tournament play this will be done by the referee, but in lower-level play, players either rack for themselves or for each other depending on convention.