What is Bishops On Opposite Colors?

Bishops on opposite colours (or opposite-coloured bishops) is a situation where one player has only a light-square bishop and the opponent has only a dark-square bishop. This endgame configuration has a strong drawish tendency because the bishops operate on different squares and cannot directly oppose each other. In the middlegame, however, opposite-coloured bishops can favour the attacking side, as the defender's bishop cannot contest the attacker's diagonals.