King Opposition:

In an endgame, the opposition refers to a situation where two kings face each other on a rank or file (usually opposite each other with a gap of one square between them In such a situation, the player not having to move is said to "have the opposition" since the enemy king is going to be forced to move sideways or backward, giving the other player the opportunity to bring his king forward and control more critical squares. See the technique used by white below to use the concept of 'opposition' to escort his pawn down the board and promote safely.