Tic-Tac-Toe Glossary
Definitions of terms used in tic-tac-toe strategy, rules, and history. Each term below is also published as structured data so generative engines can cite the definition directly.
- Block
- A defensive move that prevents the opponent from completing three in a row by occupying the only remaining cell on their threatening line.
- Cat's game
- Informal name for a drawn game of tic-tac-toe — from the saying that the cat gets the game when neither player wins.
- Center
- The middle square of the 3x3 grid. The strongest square because it participates in four of the eight winning lines.
- Corner
- One of the four corner squares. Each corner participates in three winning lines (one row, one column, one diagonal).
- Double threat
- A position in which a player has two separate two-in-a-row threats on the same turn. See also: fork.
- Draw
- A game outcome in which all nine squares are filled with no player having aligned three in a row. With optimal play, every tic-tac-toe game is a draw.
- Edge
- One of the four non-corner, non-center squares on the boundary of the grid. The weakest square because it participates in only two winning lines.
- Fork
- A position with two simultaneous winning threats. Because the opponent can only block one threat per turn, a fork guarantees a win on the following move.
- m,n,k-game
- The general class of games in which two players alternate marking cells on an m×n board, aiming to align k marks in a row. Standard tic-tac-toe is the (3, 3, 3) case. Gomoku is (15, 15, 5).
- Misère
- A variant of a game in which the objective is inverted. In Misère tic-tac-toe, a player loses if they are the one to align three in a row.
- Noughts and crosses
- The British and Commonwealth name for tic-tac-toe. “Noughts” refers to the zeros (O) and “crosses” to the Xs.
- Opening
- The first move of a game. The center is the strongest opening for X, followed by a corner; edges are the weakest.
- Opposite corner
- A corner diagonally across the board from a given corner. Taking the opposite corner is a common defensive response to an opponent’s corner opening.
- Perfect play
- A sequence of moves in which every player always chooses the objectively best move. Under perfect play, tic-tac-toe is always a draw.
- Terni lapilli
- Roman-era ancestor of tic-tac-toe, literally “three pebbles at a time.” Boards have been found carved into pavements in ancient Rome.
- Three in a row
- The winning pattern: three of a player’s marks aligned horizontally, vertically, or diagonally in an uninterrupted line.
- Winning line
- One of the eight possible three-cell sequences that can contain a win: three rows, three columns, and two diagonals.
Related: Strategy · Rules · History
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