A triplane is a fixed-wing aircraft equipped with three vertically stacked wing planes. Tailplanes and canard foreplanes are not normally included in this count, although they occasionally are.

A fixed-wing aircraft is a heavier-than-air flying machine, such as an airplane, which is capable of flight using aerodynamic lift. Fixed-wing aircraft are distinct from rotary-wing aircraft, and ornithopters. The wings of a fixed-wing aircraft are not necessarily rigid; kites, hang gliders, variable-sweep wing aircraft, and airplanes that use wing morphing are all classified as fixed-wing aircraft.