Definition of Lag

This is the state after which the person returning the break has had the opportunity to catch and even the field after the breakers advantage.

This is what is brought to the table if you are playing at your best potential.

A predetermined number of games, usually played for a specified sum of money. Contrast race (a predetermined number of wins). Informally, sets may refer to gambling more generally, as in "I've been playing sets all day", even when the format is actually races or single games.

This is to miss your shot but either luckily or on purpose leave your opponent with nothing to shoot at.

This is a special shaped leather or plastic bottle that is used on the table during play in special pocket games.

A successful attempt to get out of a snooker.

Also known as back spin, a type of spin applied to the cue ball by hitting it below its equator, causing it to spin backwards even as it slides forward on the cloth. Back spin slows the cue ball down, reduces its travel, and narrows both the carom angle after contact with an object ball, and angle of reflection off a cushion. There are several variant terms for this, including "bottom" and "bottom spin" in the US and "screw" in the UK. Draw is thought to be the first spin technique understood by billiards players prior to the introduction of leather tips, and was in use by the 1790s.

This refers to the cluster of balls remaining in a similar position to where they were within the break.

In team match play when playing one-on-one matches, if one team is short a player, a player on that team is called back to play a second match.
For example: Team A has 6 players, Team B has 4 players. There will be five individual matches played. For the fifth match Team A can pick a player from Team B to play a second match against their fifth match player.

Chiefly American: The half of the table in which the object balls are racked (in games in which racked balls are used). This usage is conceptually opposite that in British English, where this end of the table is called the top. Contrast head.

Nearly table-length distance between the cue ball and target object ball, or near cue and object balls and target pocket, i.e. a potentially difficult shot ("you sure left me a lot of green on that one").
The cloth covering the table.

Refers to a person gambling when he has no money. As in, "That jerk can't pay up, he was shooting air barrels the whole time".

In snooker, a situation during a frame in which the first line of the remaining reds grouped together, where the original pack was, are in a straight horizontal line. This has implications when opening the pack, as a full-ball contact off the top cushion will usually cause the cue-ball to stick to the red and fail to develop a potting opportunity.

A pejorative term for an improper rack in which the balls are not properly in contact with their neighbors, often resulting in a poor spread on the break.

The upper portion of a cue which slides on a player's bridge hand and upon which the tip of the cue is mounted at its terminus. It also applies to the main, unsegmented body of a mechanical bridge.

Asian Pocket Billiard Union. The APBU is a member of the WPA.

A player's turn at the table, also known as an inning.

To allow an opponent to stop playing a set for money in exchange for something. If a player is winning a set by a wide margin, with $100 on the line, the player could say, "I'll let you out now for $75." This is usually meant to save pride.

Anything that causes a foul according to the rules of a game.

The cue ball's position after a shot. "Good" or "bad" in reference to a leave describe respectively and advantageous or disadvantageous position for the next shot, or to leave an incoming opponent safe.

This is a version of double elimination tournament play that splits the field of competitors into two brackets that come together for a single elimination championship game.

This is a handicapping method where one player gets the break, and is allowed to choose any ball afterwards to put in their pocket.

The material which covers the bed and cushions of a pool table. The cloth used to cover a pool table is very special and can come in a variety of grades. Along with the general quality of the table itself, the cloth play a very important role in how a particular table plays.

Failure to hit an object ball at all with the cue ball. In most sets of rules, this is a foul like any other. However, in some variants of bar pool a table scratch while shooting for the 8 ball is a loss of game where other more minor fouls might not be, as is scratching on the 8 ball (neither result in a loss of game in most professional rules).
By way of drift from the above definition, the term is also applied by many league players to the foul in more standardized rules of failing to drive a (any) ball to a cushion, or to pocket a legal object ball, after the cue ball's initial contact with an object ball.
By way of entirely different derivation ("scratch off the table"), it can also mean knocking the cue ball (or more loosely, any ball) completely off the table.