A nightrider (also known as a knightmare or unicorn, though the latter sometimes also means the bishop–nightrider compound) is a fairy chess piece that can move any number of steps as a knight in the same direction. Intervening squares must be vacant. For example, a nightrider on b2 can reach square c4 and forward to d6 and e8, but cannot jump over the f4-pawn to reach h5. The nightrider is usually represented by an inverted knight in diagrams, and symbol N in text (in which case the knight is abbreviated as S for German Springer).