Tic-tac-toe is a game where two players X and O fill the hash (#) shaped box (consist of two vertical lines crossing two horizontal lines) with their alternate turns. The player who first fills the box with 3Xs or 3Os in a horizontal, vertical, or diagonal manner will win the game. 

In some cases, when none of the players succeeds in filling the boxes horizontally, vertically, or diagonally with 3Xs or 3Os, then the game will be considered to be a draw.