Zugzwang
Zugzwang — German for the compulsion to move — is the situation where the side to move would gladly pass, because every legal move worsens its position. With many pieces on the board it is rare, but in king-and-pawn endings it decides countless games: somebody must step aside and lose the key squares. Recognising a zugzwang position tells you when slow king moves, not checks, are the winning plan.
Black must move; after the king gives way, White takes the key squares and the d-pawn promotes.