Tick-tack-toe, Tic-tac-toe, Tick-tat-toe, or Tit-tat-toe (USA, Canada)
Noughts and crosses or Naughts and crosses (United Kingdom, Republic of Ireland, Australia, New Zealand, South Africa)
Exy-Ozys, Xsie-Osies (verbal name only) (Northern Ireland)
Xs and Os (Egypt, Republic of Ireland, Canada, Zimbabwe)
Tic-tac-toe is a paper-and-pencil game for two players, X and O, who take turns marking the spaces in a 3x3...20x20 grid. The player who succeeds in placing (n) of their marks in a horizontal, vertical, or diagonal row wins the game.
Players soon discover that best play from both parties leads to a draw. Hence, Tic-tac-toe is most often played by young children.
Because of the simplicity of Tic-tac-toe, it is often used as a pedagogical tool for teaching the concepts of good sportsmanship and the branch of artificial intelligence that deals with the searching of game trees.
The game can be generalized to an m,n,k-game in which two players alternate placing stones of their own color on an m×n board, with the goal of getting k of their own color in a row. Tic-tac-toe is the if classic (3,3,3)-game.
An early variant of Tic-tac-toe was played in the Roman Empire, around the first century BC. It was called Terni Lapilli and instead of having any number of pieces, each player only had three, thus they had to move them around to empty spaces to keep playing. The game's grid markings have been found chalked all over Rome. However, according to Claudia Zaslavsky's book Tic Tac Toe: And Other Three-In-A Row Games from Ancient Egypt to the Modern Computer, Tic-tac-toe could originate back to ancient Egypt. Another closely related ancient game is Three Men's Morris which is also played on a simple grid and requires three pieces in a row to finish.