3D Tic-Tac-Toe is an extension of the classic Tic-Tac-Toe game, played on a three-dimensional grid. Instead of a flat 3x3 board, it uses a cube made up of 27 smaller cubes, creating a 3x3x3 structure. Players take turns placing their markers, either X or O, in the small cubes, aiming to connect three of their markers in a row, column, or diagonal. The game can be played by two players, and the winning combinations can occur in various directions, including horizontal, vertical, and diagonal lines across different layers of the cube. This adds complexity and strategy compared to the traditional Tic-Tac-Toe game.