An unmanned aerial vehicle (often called a drone) is an aircraft that is not operated by a pilot on board.
Drones may have an onboard computer to take care of adjustments to wind and changes in air pressure. Sometimes they are programmed to a particular target. Important decisions are usually supervised by people on the ground communicating by radio.
Large UAVs are mostly used by military forces, for example for reconnaissance. Some of them are programmed to be a target, to be shot at. A few carry weapons for unmanned combat. Drones also have civilian uses, such as firefighting or taking photographs.