Harrwitz bishops (named after Daniel Harrwitz (1823-1884)) are bishops that occupy ajacent diagonals. For example, White has Harrwitz bishops in the Danish Gambit.
They can be very good attackers, especially in the middlegame. They are also known as raking bishops. 'Horwitz bishops' and 'Horrwitz bishops' are synonyms of Harrwitz bishops.