Definition of cluster

Two or more object balls that are touching or are close together.

24 Random Essential Billiards Terms

To play a shot using a more difficult application of stroke and speed to achieve a certain desired position for the next shot, even at the expense of or sharply increasing the likelihood of a miss.
A material, usually leather, placed on the end of a cue stick that comes in contact with the cue ball.
A shot played with stun, but not quite enough to completely stop the cue ball, allowing for a little follow. It is played so that a follow shot can be controlled more reliably, with a firmer strike than for a slow roll. It is widely considered as one of the most difficult shots in the game to master, but an excellent weapon in a player's armory once it has been.
The normal phenomenon where the object ball is pushed in a direction very slightly off the pure contact angle between the two balls. Caused by the friction imparted by the first ball sliding past or rotating against the other ball.
This is a unique game played on a table with smaller pockets. The balls are racked in a typical pyramid, but after the break any ball can be the cue ball, and you can score by hitting a ball in or by putting the ball in after bouncing it from another object ball.
A fast paced offensive game similar to 9-ball but only using balls numbered 1 through 7.
Pocketing the 7-ball wins the game. Under the current pro rules of 7-ball, any missed shot gives your opponent ball-in-hand.
Side spin on the cue ball that causes it to unnaturally roll off a cushion (contacted at an angle) against rather than with the ball's momentum and direction of travel. If angling into a cushion that is on the right, then reverse english would be right english, and vice versa. The angle of deflection will be steeper (narrower) than if no english were applied. The opposite of running english, which has effects other than simply the opposites of those of reverse english.
Also treble. A British term for a type of bank shot in which the object ball is potted off two cushions, especially by sending it twice across the table and into a side pocket. Also called a two-cushion double.
A bridge formed by the hand where no finger loops over the shaft of the cue. Typically, the cue stick is channeled by a "v"-shaped groove formed by the thumb and the base of the index finger.
This game is played on a smaller octagonal table filled with bumpers in the middle and two more bumpers surrounding a hole on each side of the table. The game is played by trying to sink the balls into the opposite pocket by hitting the object ball directly instead of using a cue ball.
Principally British: In snooker, if a player wins all of the required frames in a match without conceding a frame to their opponent - for example, if a player wins a best-of-nine-frame match with a score of 5-0 - this is referred to as a "whitewash". This term is based on a similar term used in the card game of "patience" in the UK. However, it is not used in the context of a 1-0 winning scoreline in a match consisting of a single frame.
Verb: "To Clock" To carefully note the abilities or betting inclinations of other players for future reference.
A deliberate foul that leaves the balls in a safe position, reducing the risk of giving a frame-winning chance to the opponent. The miss rule in snooker was implemented primarily to discourage the professional fouls.
This a shot that hits the object ball at the nine ball to see if you can get lucky by sinking the nine ball in any pocket. (also see Rolling the Cheese and Cheese the Nine).
Term for object balls in the game of Chicago that are each assigned as having a set money value; typically the 5, 8, 10, 13 and 15. In games where multiple balls must be pocketed in succession to score a point, such as cribbage pool or thirty-ball, when the last ball necessary to score has been potted, the points given is referred to as a way.
In the UK, one of the two pockets one either side of a pool, snooker or English billiards table halfway up the long rails.
Confederation Panamerica of Billiards
The desired angle that must be created between the path of the cue ball and the path of the object ball upon contact to pot the object ball. It is usually measured to the center of the pocket. See also aiming line.
In snooker, to leave the cue ball ball on the spot of a colour ball after potting it. This is usually performed where re-spotting of the colour ball would cause positional problems for the player, such as blocking available pots on one or more red balls.
Also bar box, pub table, tavern table. Distinctive pool tables found in bars/pubs/taverns, and often in various other venues such as family entertainment centers and arcade rooms at bowling alleys. They are almost always coin-operated and smaller than tables found in pool halls. Typical bar boxes are 3.5 ft (1.1 m) × 7 ft (2.1 m).
Also sidespin, side-spin, side. spin placed on the cue ball when hit with the cue tip to the left or right of the ball's center; usually called english in American usage. See english, in its narrower definition, for details on the effects of side spin.
Asian Pocket Billiard Union. The APBU is a member of the WPA.
In pool, the degree to which racked balls move apart upon impact by the cue ball as a result of a break shot.
In snooker, a shot sending the cue ball into the pack of red balls and separating them (after potting the ball-on). At least one split is usually necessary in each frame, since the original triangle of reds does not allow any balls to be potted reliably.

1- This is a knowledgeable shot showing skill on the movement of the cue ball.

2- This is an experienced one pocket pool player that shows extraordinary skill at coordinating the cue balls and object balls for safety plays.