V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

QDOS
       Quick and Dirty Operating System (OS, PC, MS-DOS, predecessor)


The Free On-line Dictionary of Computing (30 December 2018):

QDOS

    The Sinclair QL's proprietary operating
   system.  The origin of the name is uncertain (a weak pun on
   kudos, perhaps, as Unix was on Multics).  There was
   another OS around from the birth of personal computers called
   Q.D.O.S. - Quick And Dirty Operating System.  QDOS might also
   stand for QL Data/Disk/Drive/Device Operating System.

   QDOS did the usual OS sorts of things, as well as
   multitasking.  It was unusual in several ways.  It treated all
   devices (serial ports, mouse ports, screen, microdrive,
   disk drive, keyboard, etc.) uniformly, so you could print a
   text file direct to disk or save a binary to the screen for
   example.

   Also logical channels could be assigned to particular physical
   devices.  Output directed to a channel would go to the
   appropriate in/output.  This also meant you could have many
   windows on screen (the QL booted up from internal ROMs with 3
   windows - command line, output and program listing) all
   independent to some extent.  Channels could be redirected
   without affecting the way the process sent or received the
   data.

   (1996-07-22)