Backgammon Dictionary

A division of a tournament designed for players too strong for the novice division and who do not wish to compete in the open division.

A player of some experience who has begun to hone his skills; the level of play between novice and advanced.

A sixteenth-century game popular in England and other European countries, and probably backgammon (1)'s direct ancestor. Rolls of doubles are played just like any other roll, and there are no gammons or backgammons (2).  See: How to Play Irish.

A elimination event, usually with a large entry fee, in which only the winner and runner-up receive prize money.

The fact that an improvement in the opponent's position can make redoubling correct in a position in which the player on roll owns the cube and has one remaining chance to redouble.

[Named for Oswald Jacoby, who proposed the rule.]  A rule popular in money play which says that gammons and backgammons (2) count only as a single game if neither player has offered a double during the game. The Jacoby rule is not used in match play. The rule speeds up play by eliminating situations where a player avoids doubling so he can play on for a gammon. See post by Daniel Murphy.

A game once popular in France in which players start at diagonally opposite corners and move around the board in the same direction.  See: How to Play Jacquet.

A formula devised by Rick Janowski for estimating match equity (1) at a given score. If d is the difference in match score and t is the number of points (4) the trailing player has to go, then the probability of the leading player winning the match is .5 + .85_d_ / (t+6).  See also: Neil's Numbers and Turner's Formula.

A collection of formulas devised by Rick Janowski for estimating cubeful equity from cubeless equity. The basic formula for cubeful equity (between take points) is:

CF = CL\*(1 - x) + CE\*x

where CF is cubeful equity, CL is cubeless equity, CE is cubeful equity assuming all doubles are perfectly efficient, and x is a number between 0 and 1 that measures the cube efficiency. Typical values for x range from 0.55 to 0.8.   See also: Janowski's Takepoint Formula.

A formula devised by Rick Janowski for estimating your take point given your cubeless probability of winning the game. The basic takepoint formula is:

       2L - 1  
TP = -----------  
     2W + 2L + x

where TP is the cubeless equity of your take point, L is the average value of your cubeless losses (e.g., −1, if you can't lose a gammon), W is the average value of your cubeless wins (e.g., +1 if you can't win a gammon), and x is a number between 0 and 1 (typically 0.55 to 0.8) that measures cube efficiency. See Janowski's article, Take-Points in Money Games.

The first commercial neural-net backgammon program (1994) after TD-Gammon.   Website: Jellyfish Backgammon.

Potential for awkward rolls on a future turn.  See also: Double Jeopardy.

The standard deviation of the difference between two rollouts: JSD = sqrt(SD1*SD1 + SD2*SD2). A measure of how statistically significant the result is.

An exceptionally good roll, especially a roll that reverses the likely outcome of the game; a roll much luckier than average.

Joint standard deviation.

Affectionate name for a player's farthest-back checker.

Breaking points in your home board in hopes of getting the checkers recirculated, a back game strategy.

A position which is both a proper double and a correct beaver. This can happen only in money play with the Jacoby rule. By doubling, the underdog gets full value for his potential gammons, thus raising his equity; however, as long as this equity remains negative, the opponent should beaver.

A formula devised by Tom Keith for making cube decisions in pure race games. It is a modification of the basic pip count designed to take into account elements of checker distribution. Each player's Keith count is his pip count, plus 2 for each checker more than 1 on his one-point, plus 1 for each each checker more than 1 on his two-point, plus 1 for each checker more than 3 on his three-point, plus 1 for each empty space on points four, five, or six. Then the player on roll increases his count by one-seventh (rounding down). Keith advises: Double if your count exceeds your opponent's count by no more than 4; redouble if your count exceeds your opponent's count by no more than 3; take if doubler's count exceeds your count by at least 2. For a comparison with other methods, see the article, "Cube Handling In Noncontact Positions".

A point (1) required to complete a prime in front of the opponent's runners; the four-point, five-point, and bar-point are usually key points.