Definition of extension

Any mechanical aid that serves to extend the length of the player's cue, normally added to the end of the butt either by clipping around the end or screwing into the base. Though extensions are used for pool, it is more common in snooker because of the significantly larger table size.
In a tournament where players get limited time to make their shots (common in televised matches), an extension is extra time granted before making a shot; players have a limited number of extensions in each frame.

24 Random Essential Billiards Terms

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.
This is English that turns into running action after contact with the object ball. This will open up the angle on a bank.
To intentionally miss a shot (that results in a foul) in order to create a position for the cue ball that makes it hard for the other player to execute their shot. Not to be confused with a "Safety", since a safety is a legal hit.
This is a style of playing a pool game with a partner playing on your team. You can either take turns or play in a tag team style. This works well when there are a lot of people around that want to play.
A form of team play in which two players compete against another team of two players in any given frame or match. In a doubles game, the first player from the breaking team is the only one who shoots during the opening inning, with control of the table passing to a member of the opposing team at the end of that inning, then upon the end of the opponent's inning to the doubles partner of the original player, and next to the second opponent, play proceeding in this doubly alternating manner until concluded. Contrast Scotch doubles.
Also simply maximum. In snooker, the highest break attainable with the balls that are racked; usually 147 points starting by potting fifteen reds, in combination with blacks, and clearing the colours. Also called a 147 (one-four-seven). In six-red snooker, the maximum break is only 75 points, due to fewer red balls and thus fewer black-scoring opportunities.
A type of safety shot in the middle of a safety exchange that is not intended to put the opponent in a difficult situation regarding their next safety, but rather played so as to not leave an easy pot on. A typical example in snooker, which sees the most shots of this kind, is a slow roll-up into the pack.
A 7 inch (17.8 cm) square box drawn on a balkline table from the termination of a balkline with the rail, thus defining a restricted space in which only 3 points may be scored before one ball must be driven from the area. It developed to curtail the effectiveness of the chuck nurse, which in turn had been invented to thwart the effectiveness of the Parker's box in stopping long, repetitive runs using the anchor nurse.
A point bead on a scoring string.
The way in which a player holds the butt end of the cue stick.
The wrap of the cuestick where the hand is placed, also known as the "grip area."
Same as gapper
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.
Same as foot spot. Chiefly British today, but also an American usage ca. World War I.
British term referring to the base or metaphorical "feet" of a ball that rattles in the jaws of a pocket before eventually dropping. Usually said of an object ball for which the intention was to pot it.
Chiefly British: Short for side spin. In Canadian usage, the term is sometimes used as a verb, "to side".
This is a blemish added to the table in order to help execute a shot; these marks are not allowed and result in a foul.
American Cuemakers Association. This organization was formed in 1992 to help bring value to the development and advancement of cues in the United states.
A ball positioned near a pocket so that a particularly positioned object ball shot at that pocket will likely go in off it, even if aimed so imperfectly that if the warrior was absent, the shot would likely result in a miss. Usually arises when a ball is being banked to a pocket.
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.
One of the alternating turns players (or doubles teams) are allowed at the table, before a shot is played that concedes a visit to his/her opponent (e.g. "he ran out in one visit"). Usually synonymous with inning as applied to a single player/team, except in scotch doubles format.
See two-shot carry.
Also (chiefly British) programme. Short for shot program. The enumerated trick shots that must be performed in the fields of artistic billiards (70 pre-determined shots) and artistic pool (56 tricks in 8 "disciplines").
This is a carom shot that utilizes english and only two rails to achieve three cushion contacts.
An area defined on a billiard table, in games such as pool, snooker, English billiards and bagatelle, by a single balkline (drawn or imaginary) that runs across the table near the head (bottom) end; exactly where depends upon table type and size. This balk is where the cue ball is placed in lagging for lead, for making the opening break shot, and sometimes for other purposes, depending upon the game.
This is the act of keeping your ball location advantages the way they are, and not allowing your opponent to even things out in the game of one pocket.