An unmanned aircraft system (UAS) also referred as an unmanned aerial vehicle (UAV), is an aircraft without a human pilot on board. Its flight is either controlled autonomously by computers in the vehicle, or under the remote control of a pilot on the ground or in another vehicle.
There are a wide variety of UAS/UAV shapes, sizes, configurations, and characteristics. Historically, UASs were simple remotely piloted aircraft, but autonomous control is increasingly being employed.
They have been predominantly deployed for military applications, but are starting to be used in a small but growing number of civil applications, such as policing, firefighting, and nonmilitary security work, such as surveillance of pipelines. UASs are often preferred for missions that are too "dull, dirty, or dangerous" for manned aircraft.