1. A lever, switch, cable, knob, push-button, or other device or apparatus by means of which direction, regulation, or restraint is exercised over something.
2. In plural (a) A system or assembly of levers, gears, wheels, cables, boosters, valves, etc., used to control the attitude, direction movement, power, and speed of an aircraft, rocket spacecraft, etc. (b) Control surfaces or devices.
3. Sometimes capitalized. An activity or organization that directs or regulates an activity. See central control.
4. Specifically, to direct the movements of an aircraft or rocket with particular references to changes in attitude and speed. Compare guidance.
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use