Drones are commonly referred to as Unmanned Aerial Vehicles (UAV)whereas the entire system that allows a drone to function is a UAS (Unmanned Aerial System.) The UAV is the heart of the UAS and possesses fixed wings or either a single or multi-rotary build for flight. Lighter-than-air UAVs, such as blimps and balloons, and small “Flapping Wing” UAVs also exist.http://www.satuav.com/helicopter-drone/