A propeller shaft is a mechanical component that transmits power from the engine to the propeller in various vehicles, including boats and aircraft. It is designed to handle rotational forces and is typically made of strong materials like steel or aluminum to withstand the stresses of operation. In marine applications, the propeller shaft connects the engine to the propeller, allowing the vessel to move through water. In aircraft, it links the engine to the propeller or rotor system, enabling flight. Proper maintenance of the propeller shaft is essential for efficient performance and safety.