Reversi Terminology & Glossary
This comprehensive glossary covers every important term used in Reversi and Othello. Whether you’re reading strategy guides, watching competitive matches, or discussing games with other players, this reference will help you understand the language of the game.
Board and Setup Terms
Board
The standard 8×8 grid (64 squares) on which Reversi is played. Competitive boards are traditionally green.
Disc (Piece)
The two-sided playing pieces used in Reversi. Each disc is black on one side and white on the other, allowing it to be “flipped” to show either color.
Starting Position
The four discs placed in the center of the board before the game begins. In Othello, this is a fixed arrangement with two black and two white discs in a diagonal pattern. In classical Reversi, the arrangement may vary.
Square Notation
Squares are labeled using a letter (column a-h) and number (row 1-8). For example, d3 is column d, row 3. This is the standard way to record moves.
Corner
The four corner squares: a1, a8, h1, h8. Corners are the most strategically valuable squares because discs placed there cannot be flipped.
Edge
Any square along the four sides of the board (rows 1 and 8, columns a and h), excluding the corners.
X-Square
The four diagonal squares adjacent to corners: b2, b7, g2, g7. Generally considered dangerous to play because they offer the opponent access to the adjacent corner.
C-Square
The eight edge squares directly adjacent to corners: a2, b1, a7, b8, g1, h2, g8, h7. Playing these requires caution as they can expose corners.
Center
The four squares in the exact center of the board: d4, d5, e4, e5. The starting position occupies these squares.
Move and Rule Terms
Legal Move
A move that results in at least one of the opponent’s discs being flipped. A player must make a legal move if one is available.
Bracket (Flank / Outflank)
To place a disc such that one or more opponent discs are trapped in an unbroken line between the placed disc and another disc of the same color. All bracketed discs are flipped.
Flip (Turn / Reverse)
The act of changing a disc from one color to the other. When discs are bracketed, they are flipped to the color of the player who made the move.
Pass
When a player has no legal moves, they must pass their turn. The other player continues playing until the first player has a legal move again, or the game ends.
Game Over
The game ends when neither player can make a legal move (most commonly when the board is full). The player with more discs wins.
Draw (Tie)
When the game ends with both players having exactly 32 discs each. Draws are uncommon but possible.
Strategy Terms
Mobility
The number of legal moves available to a player. High mobility (many moves) is generally advantageous.
Potential Mobility
The number of empty squares adjacent to your opponent’s discs. Each of these could potentially become a legal move for you. Higher potential mobility suggests more future move options.
Frontier
The set of your discs that are adjacent to empty squares. A large frontier gives your opponent more potential moves and is generally undesirable.
Frontier Disc
Any of your discs that borders at least one empty square. Minimizing frontier discs is a key strategic goal.
Interior Disc
A disc that is surrounded by other discs (not adjacent to any empty squares). Interior discs do not contribute to either player’s frontier.
Stable Disc
A disc that cannot be flipped for the remainder of the game. Corner discs are always stable. Edge discs connected to a friendly corner are stable.
Unstable Disc
A disc that could potentially be flipped later in the game. Most discs in the middle game are unstable.
Semi-Stable Disc
A disc that cannot currently be flipped but might become flippable later as the board position changes.
Tempo
The concept of having the move (or forcing your opponent to move). In many positions, being forced to move is a disadvantage because it reduces your options.
Zugzwang
A position where the player whose turn it is would prefer to pass, because any move they make worsens their position. Borrowed from chess terminology.
Parity
Whether the number of empty squares in a region is odd or even. The player who makes the last move in a region has parity advantage. Critical in endgame play.
Quiet Move
A move that flips few discs and doesn’t dramatically change the position. Quiet moves are often strong because they maintain your options without creating exploitable weaknesses.
Loud Move
A move that flips many discs and dramatically alters the position. Generally less desirable than quiet moves in the opening and middle game.
Positional Terms
Wedge
Playing between two of your opponent’s discs along an edge, splitting their edge control and creating flipping opportunities.
Wall
A continuous line of same-colored discs across the board, usually along a row or column. Walls restrict mobility for the opposing player.
Sweet Sixteen
The sixteen squares in the center of the board (not on any edge). Playing within the sweet sixteen in the opening helps maintain central control.
Diagonal
One of the diagonal lines across the board. The two main diagonals run from corner to corner (a1-h8 and a8-h1) and are the longest diagonals, containing 8 squares each.
Main Diagonal
The long diagonals running from corner to corner: a1-h8 and a8-h1.
Game Phase Terms
Opening
The first ~10-15 moves of the game, where players establish position and follow studied opening theory.
Middle Game
The phase between the opening and endgame, roughly moves 15-45. Players compete for mobility, edges, and corner access.
Endgame
The final phase of the game, typically the last 15-20 moves. Players shift from positional play to exact disc-count calculation.
Book
(Also “Opening Book”) A database of studied and analyzed opening positions. Competitive players study book positions to gain early advantages.
Off-Book
A position that exits known, studied opening theory. Once players go “off-book,” they must rely on their own judgment.
Opening Terms
Diagonal Opening
An opening where Black’s first move is to a diagonal square relative to the center.
Perpendicular Opening
An opening where Black’s first move is perpendicular to the line of the initial four discs.
Parallel Opening
An opening where Black’s first move is parallel to the line of the initial four discs.
Tiger
A popular diagonal opening variation that has been extensively analyzed.
Rose
Another diagonal opening variation known for creating sharp tactical positions.
Cow
A well-studied perpendicular opening variation.
Buffalo
A perpendicular opening variation similar to the Cow.
Competitive Terms
WOC (World Othello Championship)
The annual world championship tournament for Othello, held since 1977.
WOF (World Othello Federation)
The international governing body for competitive Othello.
Rating / Elo
A numerical representation of a player’s strength, calculated based on competitive match results.
Round Robin
A tournament format where every player faces every other player.
Swiss System
A tournament format where players are paired against others with similar scores in each round.
Transcript
A record of all moves in a game, written in square notation (e.g., “d3 c5 b6 …”).
Clock (Game Timer)
A timing device used in competitive play. Each player has a set amount of time for all their moves.
Time Trouble (Time Pressure)
When a player is running low on their allotted time, potentially leading to rushed and suboptimal moves.
Computer and Analysis Terms
Evaluation (Eval)
A numerical assessment of a position, usually generated by a computer program. Positive values favor one player; negative values favor the other.
Solved Position
A position where the theoretically optimal move (and resulting score with perfect play from both sides) has been determined, usually by computer analysis.
Logistello
A famous Reversi/Othello computer program that defeated world champion Takeshi Murakami 6-0 in 1997.
Edax
A popular open-source Othello engine known for its strong play and position analysis capabilities.
Node
In computer analysis, a single position in the game tree. Programs analyze millions or billions of nodes to find the best move.
Perfect Play
Making the theoretically optimal move in every position. Computer programs can play perfectly in positions with few enough empty squares to analyze completely.
Quick Reference
| Category | Key Terms |
|---|---|
| Board | Corner, Edge, X-square, C-square, Center |
| Moves | Bracket, Flip, Legal move, Pass |
| Strategy | Mobility, Frontier, Stable disc, Parity, Tempo |
| Position | Wedge, Wall, Sweet sixteen, Diagonal |
| Phases | Opening, Middle game, Endgame |
| Competition | WOC, Elo rating, Transcript, Clock |
This glossary covers the most commonly used terms in Reversi and Othello. As you develop your game, these terms will become second nature.