Triangulation
Lose a tempo with the king to reach the same position with the opponent to move.
Triangulation is a technique where your king takes a three-move route to reach a square it could have reached in two moves. The extra move wastes a tempo so that the same position is reached with the opponent to move - who is then in zugzwang.
This is critical in positions where the result depends entirely on whose turn it is. If you arrive with your opponent to move, they are forced into a bad position. If you arrive with your turn to move, they are fine.
Triangulation only works when one king has more maneuvering space than the other. The attacker traces a triangle while the defender cannot - so the attacker loses a tempo and the defender ends up to move in the critical position.
Examples
King takes a triangular route to lose a tempo
White plays Kd3 - the first step of the triangle. The plan is Kd3-Kd4-Ke4, arriving back at e4 but now with Black to move. The Black king on d6 cannot mirror this route - it has the c6 pawn blocking its options. When White returns to e4 with Black to move, Black is in zugzwang and must give way.
Key terms
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