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

Macintosh Operating System
Mac OS

    (Mac OS) Apple Computer, Inc.'s
   proprietary operating system for their Macintosh family of
   personal computers.

   The part of the operating system that simulates the desktop is
   called "Finder."  The multitasking version of Finder was
   called "MultiFinder" until multitasking was integrated
   into the core of the OS with the introduction of System 7.0 in
   1990.

   The Macintosh series provides a built-in graphics language,
   called "QuickDraw", which provides a standard for software
   developers.

   Mac OS 8, scheduled for delivery in July 1997, included new
   human-interface features, increased system stability and
   performance, a PowerPC processor-native Finder, tighter
   integration of Internet access through panel-based
   "assistants," Personal Web Sharing and the ability to run
   Java applets and programs through Mac OS Run Time for
   Java.  Version 9.2 was the last version of the bespoke Mac
   OS.  The next version, Mac OS X is quite different, being
   based on Unix.

   See also Macintosh file system, Macintosh user interface.

   (2007-03-15)