Which of the following refers to a small unmanned aerial vehicle?

The term that specifically refers to a small unmanned aerial vehicle is "sUAS," which stands for small Unmanned Aircraft System. This designation emphasizes that the system is not only an aircraft but also encompasses the components that allow it to operate, including the ground control station, the communications links, and any associated software. The prefix "s" indicates that it is classified as small, typically relating to weight restrictions defined by regulatory bodies, such as the FAA.

On the other hand, 'UAV' (Unmanned Aerial Vehicle) is a broader term that refers to any unmanned aircraft, regardless of size. 'UAS' (Unmanned Aircraft System) also includes more comprehensive elements, similar to sUAS, but does not restrict itself to small systems. 'UA' (Unmanned Aircraft) simply refers to the aircraft itself without considering its operational system or size specifications. Thus, "sUAS" is the most accurate term for identifying a small unmanned aerial vehicle.