A drone or UAV (Unmanned Aerial Vehicle) is a totally autonomous unmanned aircraft. It is not remote controlled but can receive orders in flight. It can have various missions, both civil and military.
Unmanned submarines are sometimes referred to as submarine drones and unmanned space vessels as space drones (e.g. the Boeing X37B).
The Barracuda military drone built by EADS. © Jean-Patrick Donzey