Definition of key ball

The object ball involved in a key shot.

24 Random Essential Billiards Terms

The point on the table surface over which the apex ball of a rack is centered (in most games). It is the point half the distance between the long rails' second diamonds from the end of the racking end of the table. The foot spot is the intersection of the foot string and the long string, and is typically marked with a cloth or paper decal on pool tables.
This is a timing device for monitoring and restricting shot times for a player.
Describing a pot played at such a pace as to just reach the pocket and drop in without hitting the back.
In snooker, the second-highest value colour ball, being worth six points.
To create contact with the cue ball or an object ball.
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."
Also the hook. In snooker, a type of mechanical bridge that has only recently been endorsed by the WPBSA to allow its use in major tournament play. It is a normal rest with the head in line with the shaft, but the last foot or so of the shaft is curved. This allows players to position the curved end around an obstructing ball that would have otherwise left them hampered on the cue ball and in need of a spider or swan with extensions, which would have less control.
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.
(noun) An opening in a table, cut partly into the bed and partly into the rails and their cushions, into which balls are shot (pocketed or potted).
(verb) Send a ball into a pocket, usually intentionally.
Principally US: One or more sets, usually in the context of gambling. See also ahead race (a.k.a. ahead session) for a more specialized usage.
Principally British: Any of a group of pre-determined frames played in a match too long to be completed within a single day's play. A best of 19 frame match, for example, is generally played with two "sessions", the first composed of nine frames, the second of ten. This term is generally used only in the context of professional snooker, as matches at the amateur level are rarely played over more than nine frames. Longer matches can be split into three or four sessions.
In the APA and CPA Leagues, session refers to the season in which League play took place. There are three sessions in each League Year-Summer Session, Fall Session and Spring Session.
Same as break.
One-on-one game play.
A common aiming method in which a phantom ball is imagined frozen to the object ball at the point where an imaginary line drawn between their centers is aimed at the desired target; the cue ball may then be shot at the center of the "ghost" ball and, ideally, impact the object ball at the proper aiming contact point. The ghost ball method of aiming results in misses where adjustment is not made for collision induced throw.
Usually a one-piece cue freely available for use by patrons in bars and pool halls.
This is an object sometimes placed underneath the cue tip.
Principally British: In snooker, if a player wins a match without the need for the final session to be played (for example, if a player wins a best-of-25-frames match split into three sessions - two sessions of eight frames and one of nine - by a margin of say, 13 frames to 3), then they are said to have won the match "with a session to spare".
Also pills, tally balls and shake balls. Small, round markers typically numbered 1 through 15 or 16, which are placed in a bottle for various random assignment purposes, such as in a tournament roster, to assign order of play in a multiplayer game, or to assign particular balls to players in games such as kelly pool.
Same as back spin.
Also lows, low, low ones. In eight-ball, to be shooting the solid suit (group) of balls (1 through 7); "you're low, remember", "you're low balls" or "I've got the lows." Compare solids, reds, little, spots, dots, unders; contrast high.
This is a ball that is positioned near your pocket that can be used to kiss off of when sinking another object ball.
The ball meant to be struck and sunk in your called shot.
Pocket openings that are significantly wider than are typical and thus allow shots hit with a poor degree of accuracy to be made that would not be pocketed on a table with more exacting pocket dimensions.
This is a shot in one pocket pool where you simple aim at a cluster of balls near your opponents pocket to attempt to make something good happen out of desperation because other shots are not feasible.
This is a low bet in a game with action.