A flaperon is a type of control surface that combines aspects of both flaps and ailerons. In addition to controlling the roll or bank of an airplane like conventional ailerons, both flaperons can be lowered together to function much the same as a dedicated set of flaps would.

The pilot still has separate controls for ailerons and flaps at his disposal. A mixer is used to combine the separate pilot input into this single set of control surfaces called flaperons. The use of flaperons instead of separate ailerons and flaps can reduce the weight of an aircraft. The complexity is transferred from having a double set of control surfaces (flaps & ailerons) to the mixer.

An aircraft that uses flaperons is the RJ.03 IBIS, an experimental two-seater aircraft. The following link shows how the IBIS design implements the aileron/flap mixer.

Aerodynamics | Aircraft controls