Reversi Glossary — Every Term Explained

The Reversi terms you will see at online tables, each explained in a sentence:

Reversi: The classic two-player disc-flipping board game on an 8x8 board — the public-domain original name of the game marketed as Othello in some markets.
Disc: A two-sided playing piece, dark on one side and light on the other; 64 are used, 32 per player.
Flank: To place a disc so that one or more straight lines of enemy discs are trapped between it and one of your own discs.
Flip: Turning flanked enemy discs to your colour — mandatory for every flanked line and settled within the same move.
Legal move: A placement on an empty square that flips at least one enemy disc; anything else is illegal, and passing is only allowed when no legal move exists.
Pass: Skipping your turn because you have no legal move; two passes in a row end the game.
Corner: One of the four board corners — a disc there can never be flipped and is stable for the rest of the game.
X-square: The four squares diagonally adjacent to corners (b2, g2, b7, g7); taking one while the corner is still empty often hands the corner to the opponent.
C-square: The eight squares directly adjacent to corners but not diagonal to them; risky while the neighbouring corner is empty, less costly than X-squares.
Frontier: Your discs that touch at least one empty square — the only discs your opponent can flip next turn, so fewer is safer.
Mobility: The number of legal moves a player has; high mobility usually means control of the game.
Empty-square scoring: The common convention that empty squares left at the end are added to the winner's total, so final scores always sum to 64.

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