From the Document: "In the U.S. military, remotely piloted vehicles (RPVs) are most often called unmanned aircraft vehicles (UAVs), which are described as either a single air vehicle (with associated surveillance sensors) or a UAV system (UAS), which typically consists of an air vehicle paired with a ground control station (where the pilot actually sits) and support equipment. Although UAS are commonly operated as one aircraft paired with one ground system, the Department of Defense (DOD) often procures multiple aircraft with one ground control station. When combined with ground control stations and communication data links, UAVs form unmanned aircraft systems or UAS. [...] UAS roles and missions have evolved over time, from collecting intelligence, surveillance, and reconnaissance to performing air-to-ground attack missions. Further, some analysts predict future roles for UAS, such as air-to-air combat and combat search and rescue. However, a detailed discussion of future concepts and missions for UAS are outside the scope of this report."
CRS Report for Congress, R47067
Congressional Research Service: https://crsreports.congress.gov/