Definitions: Zugzwang

It really means something like "move-bound" in the sense that the player whose turn it is, is required to move. Chess is a "move bound" game unlike for example Go in which players have the option to 'pass' their move. In any position the side to move is technically 'Zugzwang', but that is not what we usually mean when we use the term in Chess.

Zugzwang: The player to move does not face a direct threat, but any move he does make will result in a loss of material.

"Trebuchet"
Whichever side is to move, loses

Zugzwang can occur in the middle game too.

Reinfeld Position #860
White to move

The Knight is pinned, but it is both attacked and defended 4 times. After 1. h4 Black can play a few pawn moves but then he is Zugzwang - playing either 1. ... Ke8 or 1. ... Qe8 leaves the Rook at c7 inadequately guarded, and White will play 2. b5 winning a piece.