A helicopter is an aircraft which is lifted and propelled by one or more horizontal rotors, each rotor consisting of two or more rotor blades. Helicopters are classified as rotorcraft or rotary-wing aircraft to distinguish them from fixed-wing aircraft because the helicopter derives its source of lift from the rotor blades rotating around a mast. The word 'helicopter' is adapted from the French helicopter, coined by Gustave de Ponton d'Amecourt in 1861.

As an aircraft, the primary advantages of the helicopter are due to the rotor blades that revolve through the air, providing lift without requiring the aircraft to move forward the way an airplane does. This creates the ability for the helicopter to take off and land vertically without the need for runways. For this reason, helicopters are often used to operate in congested or isolated areas where airplanes are generally not able to take off or land. The lift from the rotor also allows the helicopter to hover in one area for extended periods of time, and to do so more efficiently than other forms of vertical take-off and landing (VTOL) aircraft, making it useful in accomplishing tasks that airplanes are not able to perform.