Why anyone saw the need to hang 'system' or 'vehicle' on the end of their acronym, beats me.
The idea is that you need more than the airframe to fly it. The "system" refers to the aircraft itself, the GCS, the communications equipment, etc. To fly a Reaper, you need a Reaper itself, a Reaper GCS, and at the very least a set of line-of-sight aerials. That's a Reaper "system." The aircraft's just an aircraft, but unlike a Tornado or Typhoon, you can't fly it on its own without the rest of the system.