1. Literally, a variation on traditional chess that involves multiple boards positioned at different heights. Another name for "three-dimensional chess." No, I'm not playing 3D chess with you—I can barely play regular chess!
2. By extension, a very complicated or complex game, system, or strategy involving a deep understanding of the situation that one's opponents or adversaries lack. Everyone thinks he's an idiot for leaking that information, but he's just playing 3D chess. He's eight moves ahead of all of us. Coaching against him is like trying to play 3D chess.