50 practical terms for reading rules, comparing shots and interpreting simulator results. Definitions distinguish contact geometry from spin and outcome.
Rules and scoring
- Carom
- Contact with both other balls by the player’s cue ball; the selected discipline adds conditions for a valid point.
- Three-cushion
- The cue ball must make at least three cushion contacts before reaching the second object ball; three different cushions are not required.
- Free carom (libre)
- Carom without a cushion minimum. Official play still has restricted corner areas; “free” does not mean without rules.
- Balkline
- A discipline with marked zones limiting consecutive points while both object balls remain inside; requirements depend on the variant.
- Inning
- A player’s turn at the table, potentially containing several points before a miss or foul ends it.
- Run
- Consecutive points scored during one inning; it is not the number of cushions in a shot.
- Average
- Total points divided by total innings. Combine matches by summing both totals, not averaging their separate averages equally.
- Equalizing inning
- A final reply for the second player in formats requiring equal innings; availability depends on the competition rules.
- Break shot
- The opening stroke from prescribed spots. In UMB carom the red must be the first object ball contacted.
- Foul
- A violation such as using the wrong cue ball or an illegal contact. Failing to score alone is not every kind of foul.
Equipment
- Cue ball
- The ball the player strikes with the cue. The opponent’s cue ball is an object ball for this player.
- Object ball
- Either of the two balls other than the current player’s cue ball; one is red, the other belongs to the opponent.
- Cushion
- The resilient rail surface that rebounds a ball. Contact at its nose differs from aiming through an inlaid diamond.
- Diamond
- A fixed rail marker used as a reference. A physical mark and a system’s numerical value are different concepts.
- Cloth
- The table covering affecting motion and rebound conditions. Product, wear, installation and cleanliness matter; no universal speed correction follows from its colour.
- Cue
- The implement used to strike the cue ball. UMB rules do not impose one universal player weight or shaft material.
- Shaft
- The front section of the cue. Its construction can influence squirt; its material alone does not predict a complete route.
- Tip
- The striking end of the cue. Contact position and tip condition matter; hardness alone does not specify the spin at a later collision.
- Chalk
- Material applied to the tip to reduce slipping at contact. It reduces miscue risk but does not guarantee every off-centre stroke.
- Bridge
- The supporting hand or mechanical support guiding the shaft; stability helps make the intended cue direction repeatable.
Geometry and systems
- Ball fraction
- The apparent overlap of equal balls along the incoming line; full, half and quarter describe contact thickness, not success probability.
- Half-ball
- The cue-ball centre is aimed at the object-ball edge. Ideal no-throw geometry gives a 30° object-ball cut, not a universal cue-ball exit.
- Tangent line
- The line perpendicular to the line joining ball centres at impact; a reference for ideal stun, not every spin state.
- Contact point
- The point where two surfaces meet. A ball’s centre passes one radius away from a cushion nose, not through it.
- Mirror construction
- Reflecting a target across an effective contact line to estimate a rebound; the ideal reflection omits spin, losses and cushion deformation.
- Diamond system
- A numbered aiming convention with its own scales and stroke assumptions; different systems cannot be mixed without checking those conventions.
- Corner-5
- A system using third-rail arrival T = departure D − first-rail aim F under its specified numbering and stroke convention.
- Plus 2
- A short-rail-first reference system. The name does not mean add two everywhere; increments depend on the selected rail references.
- Five-and-half
- A named numbering system with its own departure, aim and arrival conventions; it is not simply dividing every coordinate by 5.5.
- Through-diamond aiming
- Projecting the aim line through the rail marker behind the cushion nose; this differs from hitting the nose directly opposite that marker.
Spin and impact
- Centre-ball hit
- A tip contact near the ball centre. Cloth friction can create forward roll before impact, so this is not automatically stun.
- Topspin
- Forward rotation. A high tip contact encourages it, but speed, travel and friction determine the rotation reaching the next collision.
- Backspin
- Reverse rotation relative to travel. It can decay before impact; striking below centre does not guarantee a draw result.
- Stun
- Impact with no forward or reverse rolling component. A full hit can stop the cue ball; a cut can send it along the tangent.
- Side spin
- Rotation about a vertical axis. Its effects depend on collision, speed and other rotation; left spin is not a fixed route.
- Running side spin
- Side spin that assists tangential motion at a particular cushion contact. The same spin can act differently at another cushion.
- Reverse side spin
- Side spin opposing tangential motion at the particular cushion; “reverse” is relative to that contact, not simply left or right.
- Squirt
- The cue ball’s initial sideways departure from the cue’s aim direction during an off-centre hit; distinct from later curvature.
- Swerve
- Curvature during travel caused by spin and cloth interaction, affected by cue elevation; not the initial squirt angle.
- Throw
- An object ball’s departure deviating from the line of centres because of friction during ball contact; not merely any sideways force.
Routes and diagnosis
- Ball-first
- A route contacting an object ball before the first cushion. Later events must still satisfy the selected game rule.
- Rail-first (bricole)
- A route reaching a cushion before the first object ball; it can score in three-cushion if the complete sequence is legal.
- Around-the-table
- A route family travelling around the table, often long–short–long. The name alone does not specify every contact or a valid point.
- Ticky
- A short ball–cushion interaction near a rail. The name does not require both balls to be frozen to the cushion.
- Double rail
- A route using the same rail twice. Those contacts count individually, but the complete three-cushion scoring condition still applies.
- Kiss
- An additional ball collision, often unwanted. Avoidance depends on arrival time and ball width, not merely whether drawn centre lines cross.
- Frozen
- Already touching another ball or a cushion. Special restart/contact rules can apply; a near-rail ball is not necessarily frozen.
- Massé
- An elevated-cue stroke creating a curved path through spin–cloth interaction. It need not use a completely vertical cue.
- Position play
- Choosing a shot with the resulting layout in mind; assess the leave as well as the current point without inventing a success percentage.
- Model tolerance
- Perturbed inputs tested in simulation that retain a valid result. This is model evidence, not a measured real-player scoring probability.