A fixed-wing aircraft is a heavier-than-air craft where movement of the wings in relation to the aircraft is not used to generate lift. The term is used to distinguish from rotary-wing aircraft, or ornithopters, where the movement of the wing surfaces relative to the aircraft generates lift. Fixed-wing aircraft are called airplanes in North America (the U.S. and Canada), and aeroplanes in Commonwealth countries and Ireland (excluding Canada). These terms are derived from Greek αέρας (aéras-) ("air") and -plane.''