An unmanned aircraft system (UAS) is a broader concept than just "the drone". It covers the unmanned aircraft itself plus all the equipment needed to control it remotely — the command unit and the command-and-control link between the controller and the aircraft.
The distinction matters because Regulation (EU) 2019/947 applies to the whole system, not just the airframe. Requirements on safe operation, technical condition and pilot competency address the drone together with its control equipment as one unit.