An aileron is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll, which normally results …
Boulton's 1864 paper, "On Aërial Locomotion" describing several designs including ailerons.
A 1912 Farman HF.20 biplane with single acting ailerons hinged from the rear spar. The ailerons hang down when at rest and are pushed up into position when flying by the force of the air, being pulled down by cable to provide control.
A USAF F-16 displaying its rear tailerons, which move independently of each other to provide both pitch and roll control. Note the different attack angles visible.