Aeronautics, the science and practice of aircraft flight. (An aircraft is a vehicle that is supported in flight by its own buoyancy or by the action of air on its surfaces.) The term aeronautics takes in all phases of the design, construction, and operation of both lighter-than-air craft (airships and balloons) and heavier-than-air craft (such as airplanes, helicopters, convertiplanes, autogiros, gliders, and kites). The term aviation is usually restricted to powered, heavier-than-air craft.