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1.                 From The Free On-line Dictionary of Computing (19 January 2023):
                   
   
   
                   
                     
   drain
      <jargon> (IBM) To allow a system to complete the processing of
      its current work before the system becomes unavailable.
      E.g. draining a device before taking it off-line or telling
      a web server in a server farm not to accept any new
      requests but to finish processing any requests it has already
      accepted.
      [Jargon File]
      (2005-07-18)