The Waiting Move
Part of the Basic Mates section of Coddy's Endgames journey. Lesson 13 of 26.
Everything is in place, yet there is no check: the rook's file meets the edge beside his king, and any check there is eaten. Play a waiting move - a safe rook move along the same line, or a king step that changes nothing - and he must walk into the corner himself. That forced step is zugzwang.