A rudder is a flat piece of material that helps control a boat's direction.
When you're sailing or steering a ship, the rudder is the part at the back that makes it turn. It's connected to the steering wheel by a system of ropes and levers. The rudder is usually shaped like an L or a wing, which allows it to pivot when the steering turns. As the water flows past the rudder, it creates resistance that helps push the boat in the direction you want to go.
(nautical) 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).
