rotor

A rotor is the rotating part of a helicopter which generates an aerodynamic Lift (force). The helicopter rotor, also called the rotor system, usually refers to the helicopter's main rotor which is mounted on a vertical mast over the top of the helicopter, although it can refer to the helicopter's tail rotor as well. A helicopter's rotor is generally made up of two or more rotor blades, although several earlier helicopters had a rotor with a single main rotor blade. The main rotor provides both lift and thrust, while the tail rotor provides thrust to compensate for the main rotor's torque. (information taken from wikipedia)