This glossary covers every major term used in reversi and Othello — from basic rules vocabulary that beginners need to advanced competitive concepts discussed among tournament players. Terms are organized alphabetically for easy reference.

Each definition links to the relevant strategy article where the concept is explained in depth.

A

Anchor

An existing disc of your color that “anchors” the end of an outflanking line. When you place a new disc, the anchor is the disc at the far end that completes the sandwich of opponent discs.

Anti-Reversi

A variant where the goal is reversed — the player with fewer discs at the end wins. Also called “Reversed Reversi.” This inverts standard strategy: you want to flip as few discs as possible and force your opponent to take territory.

B

Balanced Edge

An edge configuration where the discs along one side of the board are evenly split between both players, with no single player holding a dominant unbroken sequence. Compare with unbalanced edge. See edge strategy.

Black

The player who moves first. In standard Othello starting position, Black’s initial discs are at d5 and e4. Black has a slight statistical first-move advantage.

Board

The 8×8 grid of 64 squares used for play. Columns are labeled a–h (left to right); rows are labeled 1–8 (top to bottom). Squares are referenced by column-row (e.g., “a1” is the top-left corner).

Brightwell Quotient (BQ)

The official tiebreaker formula used at the World Othello Championship. Invented by British mathematician Graham Brightwell, it factors in disc count and opponent strength to break ties when players have equal points.

Buffalo Opening

A named opening sequence: d3, c5, b6. Considered risky but can yield a strong initiative for the player who employs it.

C

C-Square

The eight squares directly adjacent to corners along the edges: a2, b1, g1, h2, a7, b8, g8, h7. Playing on C-squares early is risky because it can give your opponent access to the adjacent corner. Less dangerous than X-squares but still typically avoided in the opening and midgame. See X-squares and C-squares.

Corner

Any of the four corner squares: a1, a8, h1, h8. Corners are the most valuable positions on the board because once a disc is placed in a corner, it can never be flipped — there is no way to outflank it from behind. Controlling corners is the foundation of winning strategy.

Creeping

A tactic of slowly extending your presence along an edge by playing adjacent squares one at a time, often gaining tempo while your opponent is forced to respond defensively. Related to edge strategy.

D

Diagonal Opening

The most common and well-studied opening in reversi. After Black plays d3, White responds with c3 (perpendicular to the first move), creating a diagonal tension. Leads to balanced play for both sides.

Disc

The playing piece in reversi — a flat, round token with a black side and a white side. All 64 discs are identical. When a disc is outflanked, it is flipped to show the opponent’s color.

Disc Count

The number of discs each player has on the board at any given time. Paradoxically, having a lower disc count in the opening and midgame is often strategically superior because it limits your opponent’s options.

Draw

A game that ends with both players having exactly 32 discs each. Draws are rare, occurring in roughly 1–2% of competitive games. Also called a “tie.”

E

Edge

Any of the four rows/columns along the border of the board (row 1, row 8, column a, column h). Each edge contains 8 squares. Edges are strategically important because discs on filled edges become stable. See edge strategy.

Endgame

The final phase of the game, typically the last 15–20 moves when most of the board is filled. Strategy shifts from mobility toward disc maximization and parity control. See endgame strategy.

Evaporation

A dramatic late-game swing where one player’s disc count drops rapidly as the opponent makes powerful multi-directional flips. Common when a player who held a large disc lead but poor positional structure enters the endgame.

F

Flip

The act of turning an outflanked disc from one color to the other. When you outflank opponent discs, they are flipped to your color. Also called “capture” or “turn.”

Frontier Disc

A disc that has at least one empty square adjacent to it (horizontally, vertically, or diagonally). Frontier discs are risky because they give your opponent places to outflank you. Minimizing your frontier is a core strategy principle.

G

Game Tree Complexity

The total number of possible games that can be played, a key measure of game complexity. For reversi, this is estimated at approximately 10⁵⁸ — vastly more than checkers (10³¹) but less than chess (10¹²⁰). See computer AI.

H

Hot Region

An area of the board in the endgame where both players have strong interest in playing. Hot regions contain squares where the outcome of who plays there significantly affects the final score. Contrasts with “cold regions” where the outcome is already determined.

I

Interior Disc

A disc completely surrounded by other discs on all eight adjacent squares — no empty square touches it. Interior discs reduce your frontier and therefore reduce your opponent’s options. Building interior discs is a key mobility strategy.

L

Any placement that outflanks at least one opponent disc. If no legal move exists, the player must pass. Every legal move is mandatory — you cannot choose not to flip.

Liberty

An empty square adjacent to one of your discs where your opponent could potentially place a disc to outflank you. More liberties means more vulnerability.

Logistello

The computer program that defeated reigning world Othello champion Takeshi Murakami 6–0 in 1997 — one of the first times AI decisively beat a human world champion in a strategy game.

M

Midgame

The middle phase of the game, roughly moves 15–45. Strategy focuses on mobility, positional control, and maneuvering for corner access. Disc count is relatively unimportant during this phase.

Mobility

The number of legal moves available to a player at any point. High mobility is a major strategic advantage — it gives you more options and often forces your opponent into bad moves. Maximizing your mobility while limiting your opponent’s is the central theme of intermediate strategy.

N

Noise

Informal term for moves that flip many discs in multiple directions, creating a messy board state. Noisy moves typically increase both players’ frontiers and are generally considered strategically poor in the midgame.

O

Opening

The first 10–20 moves of the game. Named opening sequences (like the Diagonal, Tiger, Rose, and Buffalo) have been studied extensively in competitive play.

Opening Book

A database of studied opening positions and their best continuations. Competitive players memorize opening books similar to how chess players study opening theory.

Othello

The trademarked name for the modern version of reversi with a fixed starting position, created by Goro Hasegawa in 1971. See Reversi vs Othello.

Outflank

To place a disc so that one or more opponent discs are trapped in a straight line between your new disc and an existing disc of your color. Outflanking triggers the flip of all trapped discs. This is the fundamental mechanic of the entire game.

P

Parallel Opening

A rare opening where White responds to Black’s first move by playing directly across (d3, d6). Leads to cramped, symmetrical positions and is uncommon at high-level play.

Parity

Whether the number of empty squares in a region (or on the whole board) is odd or even. The player who makes the last move in an odd-count region gains an advantage. Controlling parity is a critical endgame technique.

Pass

When a player has no legal move, their turn is automatically skipped. In reversi, passing is never voluntary — you must play if you can. If both players must pass consecutively, the game ends.

Perfect Game

A game ending 64–0 where one player owns every disc on the board. Also called a “wipeout.” Essentially impossible between competent players.

Perpendicular Opening

An opening where White responds at a right angle to Black’s first move (e.g., d3, c5). Leads to asymmetric, tactical positions and is popular in competitive play.

Poison Disc

A deliberately placed disc that appears advantageous for the opponent to capture but actually worsens their position — typically by reducing their mobility or forcing them onto X-squares.

Positional Play

A style that prioritizes board control, mobility, and stability over raw disc count. Virtually all strong reversi play is positional rather than greedy.

Q

Quiet Move

A move that flips very few discs (ideally just one) and keeps your frontier small. Quiet moves preserve mobility and are generally the strongest type of move in the opening and midgame. The opposite of a “noisy” move.

R

Region

A connected group of empty squares on the board. In the endgame, the board often splits into distinct regions, and who plays last in each region is determined by parity.

Rose Opening

A named opening sequence: d3, c3, c4, c5. Considered solid, leading to a balanced midgame. One of the most popular openings in tournament play.

S

Stable Disc

A disc that can never be flipped for the rest of the game, regardless of what moves are played. Corner discs are always stable. Discs on a filled edge connected to a corner are also stable. Accumulating stable discs is a primary goal of advanced strategy.

Stoner Trap

An edge formation where one player builds a 5-disc unbalanced edge that forces the opponent to concede a corner. Named after competitive player John Stoner. One of the most well-known tactical patterns in reversi.

Swindle

A move in a lost or drawn position made in the hope that the opponent will respond incorrectly, turning the game in your favor. Swindles are more effective in time-pressure situations.

T

Tempo

The ability to force your opponent to respond to your move in a specific way, giving you control of the game’s pace. “Gaining tempo” means making a move that compels a response, while “losing tempo” means being forced to react. Important in edge strategy.

Tiger Opening

An aggressive opening sequence: d3, c5, d6, c3. Favors Black. One of the most popular openings in competitive play along with the Rose.

Transcript

A record of all moves in a game, typically written as coordinate pairs (e.g., “d3 c5 d6 c3…”). Used in tournament play and for post-game analysis. The standard recording method at the World Othello Championship.

U

Unbalanced Edge

An edge where one player has five discs and the opponent has one or two, creating a formation that can be exploited (often as a Stoner trap). Unbalanced edges are a critical pattern to recognize. See edge strategy.

W

Wall

A line of stable discs along an edge, typically anchored by a corner. Building walls is the endgame payoff for securing corners — a wall of 8 stable discs along one edge represents a permanent claim on 8 squares.

Wedge

A disc placed between two opponent discs on an edge, splitting their wall. Wedges often force the opponent to give up a corner when they try to repair the split. A powerful tactical tool in edge strategy.

White

The second player. In standard Othello starting position, White’s initial discs are at d4 and e5.

Wipeout

A game ending 64–0 — one player owns every disc on the board. Also called a perfect game. Extremely rare.

World Othello Championship (WOC)

The annual international Othello tournament held since 1977, organized by the World Othello Federation. Japan has dominated the event historically. See World Championship guide.

X

X-Square

The four squares diagonally adjacent to corners: b2, b7, g2, g7. Playing on an X-square is one of the most dangerous moves in reversi because it almost always gives your opponent access to the adjacent corner. Considered the worst squares on the board in most situations. See X-squares and C-squares.