What does "unmanned aircraft" refer to?

The term "unmanned aircraft" specifically refers to aircraft that are designed to be operated without any human onboard, commonly known as drones or remote-controlled aircraft. This designation allows for various applications ranging from military use to commercial deliveries and aerial photography. The key aspect of unmanned aircraft is their operation by remote control or autonomously, rather than having a human pilot physically present in the vehicle.

Understanding what unmanned aircraft are helps differentiate them from traditional aircraft that require a crew, such as those used for passenger transport or cargo that must be piloted from within the aircraft itself. The focus on "unmanned" clarifies that these types of aircraft can operate independently of human presence, which is a significant distinction from other types of aircraft mentioned in the other options.