In simplest terms, a drone (sometimes called Unmanned Aerial Vehicles (UAVs) or Unmanned Aircraft Systems) is a spacecraft or aircraft without a pilot aboard. Drones can be controlled by a pilot on the ground with a remote system, or autonomously by an onboard computer.
The US military uses drones for missions that are deemed too risky for a human pilot. Military drones have been around since 1911, and are commonly used for for reconnaissance, surveillance and in some cases, air strikes on enemy targets. Drones are also used for research. NASA recently sent a small UAV to space for four classified missions.
Private and commercial purposes for drones might include land surveys, movie production, sports broadcasting, wildlife conservation and simple, weekend fun.