Endgames
Zugzwang
Zugzwang occurs when the obligation to move worsens your position: every legal move gives up something essential. It is especially common in endings with few pieces. Simply lacking a pleasant plan is not enough to call a position zugzwang.
A practical example
A king guards the critical entry square in a pawn ending. If it must move and no pawn move preserves the position, it must abandon that square. The same arrangement with the other side to move may have a different result.
A common mistake
Playing an unnecessary pawn move and using up the last reserve tempo. Also remember: a player with no legal move who is not in check is stalemated, rather than losing through zugzwang.
Try this in your next review
Examine an ending with White to move, then Black to move. State which defensive duty each possible move gives up. Look for waiting moves that preserve that duty.