Ultimate Tic-Tac-Toe is a strategic twist on the classic game of Tic-Tac-Toe. It consists of a 3x3 grid of smaller Tic-Tac-Toe boards, making a larger 9-square grid. Players take turns placing their symbol (either X or O) in one of the smaller boards, but the location of their move determines which smaller board their opponent must play in next. The game ends when a player wins three of the smaller boards in a row, either horizontally, vertically, or diagonally. This adds layers of strategy, as players must think about both their own moves and how to block their opponent's potential wins across the larger grid.