Backgammon Dictionary

See: Duplicate Backgammon.

A position in which the same number can be used constructively in more than one way. For example, when your opponent can use a 5 to hit either of two blots, his 5's are said to be duplicated. All else being equal, a position which duplicates the opponent's good numbers is better than one which does not because it means the opponent has fewer good rolls in total. See post by Simon Woodhead.

A backgammon variant in which the players start with all their checkers off the board.  See: How to Play Dutch Backgammon.

[Coined by Danny Kleinman in Double Sixes from the Bar.]  The negative impact on flexibility of having spare checkers exactly six pips apart.

The first few moves of a game, before the players have settled on a particular game plan.

A comparison of the cost of doubling slightly before opponent's drop point versus doubling slightly past opponent's drop point. This number varies depending on the score of the match, the level of the cube, and the chance of gammon in the current game. It is useful in determining how aggressively a player should double to avoid losing his market.

The open point directly in front of a prime.

The average number of rolls required to bear off all your checkers multiplied by the average pip value of a roll (49/6 pips). A player's EPC is equal to his actual pip count plus the wastage of the position. For more information, see article by Walter Trice and post by Douglas Zare. The EPC is also known as the Trice Count in honor of Walter Trice (1949–2009).

A double made at or near the point of maximum effectiveness, when the opponent would be correct to either accept or refuse.

To abandon an ace-point game to avoid losing a backgammon (2) or a gammon.

A tournament event in which half the competitors are eliminated each round until just one player remains.  Compare: Round Robin Format.

A method of rating players devised by Arpad Elo for the U.S. Chess Federation in 1960. Most backgammon ratings systems are based on Elo's method; for example, see FIBS rating formula.

Equivalent-to-money-game equity.

The phase of a game which starts when either player begins to bear off.

To move a checker from the bar to an open point in the opponent's home board according to a roll of the dice. When a player has a checker on the bar, this is his only legal move.

Effective pip count.

The value of a position to one of the players. Equity is the sum of the values of the possible outcomes from a given position with each value multiplied by its probability of occurrence. It is the same as the fair settlement value of the position. Your equity is the negative of your opponent's equity. See post by Gary Wong. Equity comes in different flavors.  See: Cubeless Equity, Cubeful Equity, Match Equity, and EMG Equity.

Cubeful equity normalized by transforming it linearly so that winning a single game at the current value of the cube is reported as +1 and losing a single game at the current value of the cube is reported as −1. EMG equity is commonly used in match play to compare the size of errors in different games. See the Snowie Support FAQ for a further description and an example.

ER stands for Error Rate. Playing ER backgammon means playing with a view to making the least errors from the outset rather than deliberately making suboptimal plays to steer the game toward a position that your opponent will misplay or doesn't understand.

A measure of the average equity lost per move due to errors in play. The lost equity can be measured either in match-winning chances or EMG equity. Different programs compute error rate differently: Snowie divides by the total number of moves and reports the rate in "millipoints per move." Gnu Backgammon divides by the number of unforced plays. See post by Gregg Cattanach.