(1) (nautical) steering mechanism consisting of a hinged vertical plate mounted at the stern of a vessel
(2) A hinged vertical airfoil mounted at the tail of an aircraft and used to make horizontal course changes
- An underwater vane used to steer a vessel. The rudder is controlled by means of a wheel, tiller or other apparatus (modern vessels can be controlled even with a joystick or an autopilot).
- A control surface on the vertical stabilizer of a fixed-wing aircraft or an autogyro. On some craft, the entire vertical stabilizer comprises the rudder. The rudder is controlled by foot-operated control pedals.