Quoridor Glossary
Quoridor has a small vocabulary and almost none of it is standardised, so the same shape gets three names depending on who you learned from. This page fixes the meanings used across this site. Each entry says what the word means and nothing more — the reasoning, the arithmetic and the worked examples live on the page each entry points to. If you are here because a strategy article used a term without stopping to define it, this is the stop it skipped.
Definitions assume the standard two-player game on a nine-by-nine board; where the four-player variant changes something, the entry says so. For the formal statement of any rule mentioned here, see The Complete Rules.
Baseline
The edge of the board a pawn starts on. Each pawn begins on the middle square of its own baseline and runs for the opposite edge, so your baseline is your opponent's goal edge and theirs is yours. In the four-player game all four edges are somebody's baseline. See The Complete Rules.
Blocking rule
The restriction that no wall may be placed if it would leave any player with no route at all to their goal edge. It is tested against the board as it stands at that moment, and it says nothing about how long the surviving route is. The Complete Rules gives the formal statement; Traps and Cages is built on what that silence permits.
Cage
A structure of individually legal walls that leaves a pawn's only remaining exit somewhere inconvenient, usually behind it. A cage never traps anybody — the blocking rule guarantees the exit exists — it only makes the way out long. Traps and Cages prices cages and names the tells that let you step out before one closes.
Corridor
A lane of squares narrowed on both sides — by walls, by the board edge, or by one of each — so that a pawn travelling down it has no cheap way to step sideways. Where a shoulder is a single open square beside a route, a corridor is a stretch of route with none on either side. Wall or Advance names a pawn committed to a corridor as one of the signs that a wall is worth searching for at all.
Detour
The extra squares a wall or a structure adds to somebody's route: the difference between the path they were walking and the shortest path still open to them after the wall goes down. It is the unit the rest of the vocabulary is priced in. Wall or Advance covers how to read a detour before you commit to the wall that creates it.
Elo
The rating system used to express playing strength as a single number, adapted from chess: your expected score against an opponent follows from the gap between the two ratings, and each result moves your number by the difference between what you scored and what you were expected to score. The FAQ covers how this site applies it and which games are rated; Bots carries the current bot numbers.
Fence
Another name for a wall — the physical Quoridor set calls the pieces fences, and plenty of players and older writing use the two words interchangeably. This site says "wall" everywhere. See Wall.
Fence post
A wall placed as an anchor rather than as an obstacle: one that adds nothing to anybody's path on its own, but gives a later wall an end to attach to. It is the piece a multi-wall structure is started from. Traps and Cages explains when a fence post's return stops being zero, and how to recognise one aimed at you.
Goal edge
The far side of the board a pawn is trying to reach — the whole edge, not one particular square on it. Because the target is an edge and not a cell, a pawn's distance depends on its row and not on which column it is standing in. See The Complete Rules for the win condition and Tempo and the Race for how distance is counted.
Groove
The channel between two adjacent rows, or between two adjacent columns, in which walls sit. Walls occupy the gaps between squares rather than the squares themselves, which is why a placement is named by its groove instead of by a cell coordinate. A groove is not reserved to a single wall: a wall takes only the two-square span it covers, and up to four non-overlapping walls can share one groove — but the span it takes is gone permanently. The Complete Rules has the placement restrictions; Wall Economy prices what each placement deletes.
Jump
What happens when an opponent's pawn is standing in the square you would step into: it does not block you, and instead of stopping you pass over it and land beyond. Where the square beyond is unavailable, a diagonal landing beside the pawn takes its place. The Complete Rules sets out exactly when each case applies; Openings covers what a jump is worth to the player who collects one.
k and j
The two quantities a wall is judged by: k is the number of squares it adds to your opponent's shortest path, and j the number it adds to your own. Both are counted with the hypothetical wall on the board. Wall Economy derives what the pair has to add up to before a wall beats a step.
Mainline
The default line of play in a position — what both sides do when neither has a reason to do anything else. In Quoridor's opening that is the straight advance down the centre column. Openings works out why, and what breaks the symmetry when both players play it.
Margin
The gap between the two players' arrival times in a race neither side can change any more, measured in plies rather than turns. It is the quantity that tells the leader what they can still afford. Endgames derives it, converts it into spendable turns, and shows why it always comes out odd.
Meeting square
The position, reached in the common opening where both players march straight at each other, in which the two pawns stand on the same column with exactly one empty square between them. Openings works through the choice it forces on the player to move.
Parity
The fact that each player can only ever finish on their own alternating half-moves — one player always arrives on an odd ply, the other always on an even one — and that nothing either player does changes which. Endgames proves it and turns it into a usable number.
Path length
How many moves a pawn needs to reach its goal edge along its shortest available route. It is not the number of squares between you and the far side in a straight line, because walls bend routes, and it has to be recounted every time a wall goes down. Tempo and the Race has the fast method and the cases where the fast method lies.
Ply
One half-move — a single player's turn. Plies are the right unit whenever you need to compare two arrivals exactly, because turns alternate and a "turn" as players usually count it contains one of each. Endgames switches to plies for precisely that reason.
A region of the board a pawn has walked into where the ways out are already scarce, before any wall has closed them. A pocket is the precondition for a cage rather than the cage itself: the walls are not all down yet, but the position has stopped offering cheap alternatives. Traps and Cages covers how to notice you are standing in one.
Race
The framing that treats a Quoridor position as two numbers heading toward zero — your path length and your opponent's — rather than as a maze to navigate. How to Play introduces the habit; Tempo and the Race makes it exact.
Rollout
Also called a playout: one complete game played out at speed from the position under consideration, using a cheap fixed policy for both sides, purely to see who wins it. About describes how the engine uses them.
Shortest path
The route to your goal edge that takes the fewest legal moves, given the walls currently on the board. There is often more than one: path length is a single number, while the shortest path is one of possibly several routes that achieve it. Tempo and the Race covers how to find it and how to find the alternatives at the same time.
Shoulder
The open square beside a pawn's route that a detour steps into. A pawn standing in open ground has one on each side; a board edge or a wall already on the board can remove one. Wall or Advance builds its entire search rule on counting them.
Tempo
A turn, considered as a resource you spend. Because you cannot pass in Quoridor, every turn is spent on something, so tempo is read as a comparison against what a plain step forward would have done. Strategy sets tempo against terrain as the two things a turn can buy; Tempo and the Race folds the turn into a count.
Terrain
Walls, considered as a resource — distance imposed on somebody else rather than distance you cover yourself. The word marks the fact that a wall stops being yours the moment you place it and belongs to the board thereafter. Strategy develops the contrast with tempo.
Tier
A difficulty setting on the standard bot ladder. There are six — beginner, intermediate, advanced, expert, master and extreme — and alongside them the roster carries one further opponent, an experimental neural engine that sits outside the ladder. Bots has the roster and the current ratings; the individual pages, from Beginner to Extreme, cover what each one is like to play.
Wall
The two-square piece you place in a groove to block movement across it. Each player in the standard game has ten, and a wall is never moved or recovered once it is placed. Also called a fence. The Complete Rules has the placement restrictions in full.
Wall economy
The study of what a wall actually buys — the exchange rate between spending one and simply stepping forward, how that rate moves over the course of a game, and what the walls still in your hand are worth. Wall Economy is the page that derives all three.
Wall slot
A place on the board a wall could legally go: an intersection of grooves plus an orientation. An empty nine-by-nine board offers 128 of them. The bots here do not weigh every one: Expert covers how the search narrows that list to a shortlist of candidates, while Strategy explains why pricing a candidate and generating one are different skills.
Wall supply
The walls a player has not yet placed. Ten each in the standard two-player game, five each in the four-player variant, with no way to gain more. The Complete Rules states the supply; Wall Economy covers what running out first actually costs, which is optionality rather than material.
If a term you were looking for is not here, it is most likely covered in place: The Complete Rules for anything mechanical, How to Play for the shape of a first game, and Strategy for the ideas the six deeper articles are built on. The FAQ answers the questions about the site itself rather than the game.