Glossary

The backgammon glossary

80 terms you will meet at the board and in the analysis of a match: how checkers move, how games are scored, when to double, what strategies are called and what an engine's numbers mean. Each definition is short enough for a beginner and precise enough for an experienced player.

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Board & moves27
Game & scoring11
Doubling cube12
Strategy11
Analysis19

A

AnchorBoard & moves: A point you hold with two or more checkers inside your opponent's home board. An anchor gives your back checkers a safe landing spot and a base to fight from; the further forward it sits (your 20- or 21-point), the more useful it usually is.
Away (2-away, 3-away…)Game & scoring: The usual way to state a match score: by the points each player still needs. At 2-away 4-away, you need 2 more points to win and your opponent needs 4. A player who needs a single point is 1-away, at match point.

B

Back checkersBoard & moves: The two checkers that start the game on your opponent's 1-point (your 24-point), and more generally any checker still stuck in the opponent's home board. They have the longest way to go, so escaping or anchoring them is an early priority.
Back gameStrategy: A plan for a position far behind in the race: you hold two or more anchors in the opponent's home board and wait for a shot while they bring their checkers in. It needs good timing and carries a real risk of losing a gammon.
Backgammon (triple win)Game & scoring: The name of the game, and also its biggest win: the loser has borne off no checker and still has at least one on the bar or in the winner's home board. It counts three times the value of the cube.
BarBoard & moves: The raised strip that splits the board in two. A checker that gets hit is placed on the bar and must enter the opponent's home board before its owner may move anything else.
Bar pointBoard & moves: Your 7-point, the first point outside your home board, right next to the bar. Together with your 6- and 8-points it forms a strong block in front of the opponent's back checkers.
Bear-offBoard & moves: The final phase: once all 15 of your checkers are in your home board, you take them off the board with your rolls. The first player to bear off every checker wins. A checker hit during the bear-off must travel all the way back before you can resume.
BeaverDoubling cube: An optional money-game rule: a player who is doubled may take and immediately turn the cube again while keeping it on their side, so the stake becomes four times what it was. Beavers are not used in matches.
BlitzStrategy: An all-out attack: you hit the opponent's checkers in your home board again and again while making points, aiming to close your board with their checkers on the bar. A successful blitz often wins a gammon.
BlotBoard & moves: A single checker standing alone on a point. An opposing checker that lands on it hits it and sends it to the bar. Leaving few blots within the opponent's reach is the basis of safe play, though the risk is sometimes worth taking (see slot).
BlunderAnalysis: A serious mistake: on Megammon, any decision that loses 0.080 equity or more compared with the best one (a threshold chosen by Megammon). Each blunder is flagged in the analysis with its main cause, then turned into a training exercise.
BuilderBoard & moves: A spare checker placed within reach of a point you want to make, usually in your outer or home board. The more builders aim at a point, the more rolls make it next turn (see diversification).

C

CheckerBoard & moves: One of the 15 round pieces each player moves around the board, also called a stone or a man. The game goes to the first player who bears off all of theirs.
Closed boardBoard & moves: All six points of your home board are made. An opposing checker on the bar cannot enter at all and has to wait, which is why closing the board (a closeout) is often the decisive moment of an attack.
ContactBoard & moves: Any position in which the two armies have not yet fully passed each other, so checkers can still be hit or blocked. Once contact is broken, the game turns into a pure race.
Crawford ruleGame & scoring: Match rule: in the first game after a player comes within one point of winning, their opponent may not double. That one game is the Crawford game; the cube comes back into play afterwards (post-Crawford). Megammon applies the rule and flags the Crawford game during play.
Cube ownershipDoubling cube: Who has the right to double next. At the start the cube is centered and either player may double; after a take, it belongs to the taker alone. Owning the cube is an asset, since you decide whether and when the stakes go up again.

D

DanceBoard & moves: To fail to enter from the bar: neither number rolled leads to an open point in the opponent's home board, so the whole turn is lost. The more points the opponent has made at home, the more often you dance.
DiversificationStrategy: Spreading your builders so that as many different numbers as possible are useful to you next turn. It is the mirror image of duplication: you diversify your own numbers and duplicate your opponent's.
DoubleDoubling cube: To offer, before rolling, to play the rest of the game for twice the current stake. You may double only when the cube is centered or on your side. Your opponent must then take or pass.
Double match point (DMP)Game & scoring: Both players need one point: whoever wins the next game wins the match. Gammons no longer matter and the cube plays no part, so the game is played purely to win it.
DoublesBoard & moves: A roll showing the same number on both dice, such as 4-4. You play that number four times instead of twice. For the opening roll each player throws a single die, so the very first move of a game is never played with doubles.
Doubling cubeDoubling cube: The large die marked 2, 4, 8, 16, 32 and 64 that keeps track of the stake. It starts in the middle at 1 (usually showing 64), and each accepted double moves it to the side of the player who took, at twice its previous value.
DoubtfulAnalysis: On Megammon, a decision that loses at least 0.020 but less than 0.040 equity compared with the best one. These thresholds are Megammon's choice; from 0.040 on, the decision counts as an error.
DuplicationStrategy: Arranging your checkers so that the numbers your opponent needs for one good play are the same numbers they need for another. If their 4s both hit your blot and cover their own, their other numbers do neither, and fewer of their rolls work.

E

Elo ratingGame & scoring: A rating that rises when you win and falls when you lose, by an amount that depends on the gap between your rating and your opponent's. On Megammon, every ranked online match moves your Elo, weighted by match length; it appears after five placement matches, during which it moves four times faster.
EnteringBoard & moves: Bringing a checker from the bar back into play, in the opponent's home board: a 3 enters on their 3-point (your 22-point), a 5 on their 5-point, and so on, as long as that point is not blocked. While you have a checker on the bar, you may not move any other.
EquityAnalysis: What a position is worth on average to a player, in points, with the cube at 1: +1.000 is a certain single win, −1.000 a certain single loss, and gammons push it further. Comparing the equity of candidate moves shows what each decision gains or costs.
ErrorAnalysis: On Megammon, a decision that loses at least 0.040 but less than 0.080 equity compared with the best one (thresholds chosen by Megammon). With an account, your errors and blunders become training exercises.
Error rateAnalysis: A general name for how much equity a player gives away, either in total over a match or on average per move, often in thousandths of a point. Conventions vary from one program to another; PR is a standardized form of it.

F

FlexibilityStrategy: How many different rolls your position can play well. Spare checkers spread over varied points, rather than tall stacks or checkers out of play, keep a position flexible.

G

GammonGame & scoring: A win in which the loser has not yet borne off a single checker. It counts double: 2 points with the cube at 1, 4 with the cube at 2, and so on. Whether it is worth chasing depends on the gammon value.
Gammon valueDoubling cube: How much a gammon is worth compared with a single win. In a money game it never changes: a gammon is always worth two single wins. In a match it depends on the score: a player who needs one point gains nothing from a gammon, while a player two points short wins the match with a gammon at a cube of 1.
Golden pointBoard & moves: Your 5-point, the most valuable point to make early: it blocks the opponent's back checkers, supports attacks in your home board and is hard to build later on. Held as an anchor, the opponent's 5-point is often called the golden anchor.

H

HitBoard & moves: To land on an opposing blot, which sends that checker to the bar. The hit checker loses all the ground it had covered and must enter again before its owner can play anything else.
Holding gameStrategy: Keeping an advanced anchor (on the opponent's 4-point, 5-point or bar point) while behind in the race, to keep a chance of hitting a late shot as the opponent's checkers come home past it.
Home boardBoard & moves: The six points (1 to 6) in the last quarter of your path, where all your checkers must gather before you may bear off. Also called the inner board. Points made there stop the opponent from entering from the bar.

J

Jacoby ruleDoubling cube: A common money-game rule: gammons and backgammons count only as single wins unless the cube has been turned during the game. It encourages early doubling and speeds play up. It does not apply in matches.

L

LuckAnalysis: For each roll, the difference between the equity of the roll you got and the average over the 36 possible rolls. Added up over a match, it shows how much the dice helped or hurt each player, apart from the quality of their play.
Luck ratingAnalysis: Megammon's measure of how kind the dice were: your average luck per roll, in thousandths of equity. +20 means each roll gave you on average 0.020 more than an average roll. Megammon shows it next to the PR, on its own scale from very unlucky to very lucky.

M

Made pointBoard & moves: A point occupied by two or more of your checkers. The opponent may not land there, so a made point is both safe for you and a wall against the other side. Several made points in a row form a prime.
Market loserDoubling cube: A sequence (a roll for you, then a reply by the opponent) after which your position becomes too strong for the opponent to take. When such sequences are frequent, you should double now, while a take is still possible; otherwise you lose your market.
MatchGame & scoring: A series of games played until one player reaches an agreed number of points, such as 5 or 7. The score changes what gammons and the cube are worth, so the right play at 2-away 4-away can differ from the right play in a money game. On Megammon, ranked online matches are played to 1, 3, 5 or 7 points, and matches against a friend or the bot to anything from 1 to 13.
Match equity table (MET)Analysis: A table giving each player's MWC at the start of a game, for every match score. Engines use it to turn the possible outcomes of a game (single win, gammon or backgammon, at a given cube value) into match winning chances. Several tables exist, computed in different ways.
Match pointGame & scoring: A score at which a player needs just one more point to win the match: they are 1-away. The first time a player gets there, the next game is played under the Crawford rule; when both players are there, the score is double match point.
MidpointBoard & moves: Your 13-point, in the opponent's outer board, where five of your checkers start. It works as a relay for bringing checkers home and as a safe landing spot. It is your opponent's 12-point.
Money gameGame & scoring: Games played one at a time, each settled on its own, usually for a stake per point, with no target score. Cube decisions depend on the position alone, since there is no match score to weigh; the Jacoby rule often applies.
MWC (match winning chances)Analysis: The probability of winning the whole match, given the score, the cube and the position. In a match it is the true measure of a decision: the same mistake usually costs more MWC late in the match or with the cube high. Megammon shows the MWC each decision loses.

N

Neural networkAnalysis: The kind of program at the heart of modern backgammon engines: trained on enormous numbers of games, it estimates the chances of winning, of winning a gammon and so on for any position in a fraction of a second. The Megammon Engine evaluates every position and every move with one.
Normalized equityAnalysis: In a match, a position's value converted into money-game units at a cube of 1, so that mistakes can be compared from one score to another. Megammon can show every mistake either in normalized equity or in MWC.

O

Outer boardBoard & moves: The quarter of the board holding your points 7 to 12, on the other side of the bar from your home board. Most of your builders wait there before moving into your home board.

P

Pass (drop)Doubling cube: To refuse a double: you concede the game on the spot and lose its value before the double (1 point with a centered cube). Passing is right when your chances are below the take point.
PipBoard & moves: One point of movement. A roll of 6-3 moves your checkers nine pips in all, and 5-5 moves them twenty. Distances on the board and racing comparisons are measured in pips.
Pip countBoard & moves: The total number of pips your checkers still have to travel to bear off: each checker's point number, added up (a checker on the bar counts 25). Both players start at 167, and in a race the lower count is ahead. During play, Megammon shows both pip counts by default; the analysis shows them too.
Ply (3-ply)Analysis: How far an engine looks ahead. At the lowest level the neural network judges the positions directly; each extra ply, slower but stronger, examines the 21 different rolls of the next turn and the best reply to each. In Megammon's numbering, 1-ply is the network alone, and every decision is analyzed at 3-ply.
PointBoard & moves: One of the 24 narrow triangles on which checkers stand. Each player numbers them from their own side: your 1-point is the deepest point of your home board, and your 24-point is your opponent's 1-point. A point with two or more of your checkers on it is a made point.
Position IDAnalysis: A compact 14-character code that records only where the checkers stand; it comes with a 12-character Match ID for the cube, the score and the dice. Megammon's Position page accepts a Position ID together with its Match ID.
Post-CrawfordGame & scoring: The games that follow the Crawford game. The leader needs one point, so owning the cube is worth nothing to them; the trailer therefore normally doubles as early as possible.
PR (Performance Rating)Analysis: A measure of playing quality: the average equity lost per non-trivial decision, times 500 (Megammon's definition). Lower is better, and 0 means every decision matched the engine's. Megammon shows each player's PR after every analyzed match, split between checker play and cube decisions, with a level on its own scale.
Practice modeAnalysis: A Megammon option for games against the bot or a friend: every move of both players is graded live at 3-ply, the best move is drawn on the board, and each player's PR updates as the game goes on.
PrimeBoard & moves: A wall of consecutive made points. The longer the prime, the harder it is to get past; a full prime of six points in a row cannot be crossed at all. Trapping checkers behind a prime and walking it forward is the plan of the priming game.
Priming gameStrategy: A plan built around a prime: you trap one or more opposing checkers behind a wall of consecutive points, then move the wall forward towards your home board until their position falls apart or they are closed out.

R

RaceBoard & moves: A position without contact: both sides have passed each other and nothing can be hit any more. The game is then decided by the dice, the pip count and how efficiently each side bears off.
RedoubleDoubling cube: A double offered by the player who owns the cube, for example turning it from 2 to 4. The player who receives it faces the same choice as before: take or pass.
RolloutAnalysis: Settling a position by playing it out to the end many times, with the engine choosing the moves for both sides and the dice changing every time, then averaging the results. It is the most reliable way to decide a close call. Megammon settles close decisions by rollout.

S

Safety playStrategy: A move that gives up a little efficiency or attacking power to reduce a risk: leaving fewer shots, avoiding a gammon or locking up the win. It comes up often in the bear-off against an opponent who still holds an anchor.
ShotBoard & moves: A chance to hit a blot, counted in rolls out of 36. A direct shot is at six pips or less, within reach of a single die; an indirect shot is seven pips or more away and needs both dice combined. Counting shots before leaving a blot is one of the core skills of the game.
Single gameGame & scoring: A win in which the losing player has already borne off at least one checker. It is worth the value of the doubling cube: 1 point if the cube was never turned.
SlotBoard & moves: Placing a single checker on a point you want to make, planning to cover it with a second checker next turn. Slotting accepts the risk of being hit in exchange for a quicker shot at a key point such as the golden point.
SplitBoard & moves: Moving your two back checkers apart, for instance from your 24-point onto two different points. Splitting gives you more rolls to make an anchor or to hit, at the cost of blots the opponent may attack.

T

TakeDoubling cube: To accept a double: the game goes on at twice the stake and you now own the doubling cube, so only you can redouble later. Taking is right when your chances are above the take point.
Take pointDoubling cube: The minimum winning chances that make a take correct. In a money game with no gammons and no further cube action it is 25%: below that, losing 2 points too often costs more than passing for 1. Owning the cube lowers it a little; gammons and the match score move it.
TempoStrategy: Time taken away from the opponent. Hitting for tempo, for instance, forces them to spend part of their next roll entering from the bar, so they cannot use the whole roll to attack you.
TimingStrategy: Your ability to keep your key points while you wait: having enough spare checkers and pips to play your rolls elsewhere. The side with poor timing is forced to break its prime or anchors before the opponent has to break theirs.
Too good to doubleDoubling cube: A position so strong, usually because of high gammon chances, that doubling would be a mistake: the opponent would rightly pass and you would collect 1 point, while playing on is worth more on average. You keep the cube and play for the gammon.
Truncated rolloutAnalysis: A faster rollout that stops each game after a set number of moves and lets the neural network estimate the rest. Megammon's analysis levels 1T to 3T are truncated rollouts, and its Go deeper button reruns any decision as a 3T rollout.

W

WastageStrategy: The pips lost in the bear-off when part of a roll cannot be used efficiently, for example because checkers are piled on the low points. Because of wastage, two positions with the same pip count can need a different number of rolls to bear off.
Weakness profileAnalysis: A Megammon feature that looks across all your analyzed matches and ranks your top three weaknesses by the equity they cost you, not by how often they occur, broken down by game phase and by cube decision.

X

XGIDAnalysis: A one-line text code that describes a complete position: where every checker stands, the cube, whose turn it is, the dice, the score and the match length. Paste one on Megammon's Position page to analyze it; the analysis also shows the XGID of every position, ready to copy.

Now put the words on the board.

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