Source : Free On-Line Dictionary of Computing

Record Management Services
     
        (RMS) A set of {operating system} procedures that is called by
        programs to process files and records within files.  {VMS} RMS
        allows programs to issue GET and PUT requests at the record
        level (record I/O) as well as read and write blocks (block
        I/O).  VMS RMS is and integral part of the system software;
        its procedures run in {executive mode}.