Triangulation is an endgame tactic where you aim to put the opponent in zugzwang (a position when it is a disadvantage to move). Triangulation is also called losing a tempo or losing a move. This technique usually occurs in endgames with  kings and pawns left on the board, when one king can maneuver on three adjacent squares in the shape of a triangle and maintain the basic position while the opposing king only has two such squares. See the example below: