Adjacent square

Two squares are adjacent when they touch along an edge or at a corner. A central square has eight adjacent squares, an edge square has five, and a corner square has three. This relationship depends only on board geometry, not on the pieces in the position.

A king normally moves to an adjacent square, but not every neighboring square is available. The destination cannot contain a friendly piece or be under enemy attack. This is also why the two kings may never stand next to each other: each would attack the other's square, so the move would not be a legal move.