The opposition is when the two kings stand on the same line with one square between them, and whoever has to move must give ground — so you want the move to be the opponent’s.
When the kings face off a single square apart (the direct opposition), the player to move has to step aside and let the enemy king advance. ‘Having the opposition’ means it’s the other side’s turn, so they’re the ones forced to back up.
It’s the single most important king-and-pawn idea: in countless endings, the side that wins the opposition shoulders the enemy king away from the squares it needs to defend, and the extra pawn (or the breakthrough) decides.
There’s also the distant opposition — kings further apart on the same file, rank or diagonal with an odd number of squares between them — which works the same way once the kings march toward each other.
Move your king onto the same file (or rank/diagonal) as the enemy king with one empty square between them, leaving it as the opponent’s turn to move. Then they have to step aside.
The opposition is the specific king-versus-king tool; zugzwang is the general idea of being harmed by having to move. Winning the opposition is how you put the enemy king in zugzwang.
BetterChess is a practice tool — we make no guarantee you'll reach 1800 or any rating. Definitions are standard chess terminology; every diagram position is checked legal with the same engine the board runs.