A rudder is a flat piece of material, usually made of wood or metal, that is attached to the back of a boat or ship. Its primary function is to steer the vessel by directing the flow of water. When the rudder is turned, it creates a difference in water pressure on either side, causing the boat to change direction. Rudders are commonly found on various types of watercraft, including sailboats, motorboats, and ships. They can be operated manually or automatically, depending on the design of the vessel. Proper rudder function is essential for safe navigation and maneuverability in water.