Tic Tac Toe
game played on a three by three grid by two players. One player begins by marking either an O or an X in any space on the grid. The second player then must place the other mark upon a different grid coordinate. Play alternates until one player has achieved creating a row of three. The advantage indelibly goes to the player who goes first.
A more difficult version is played in three dimensions, usually with three grids laid side by side.
The game is also known as 'noughts and crosses', particularly in the UK.