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Definition: macOS

The name of Apple's Mac operating system, starting with the Sierra Version 10.12 in 2016. Since its introduction in 1984, Mac operating systems have been written for three hardware lines: Motorola, PowerPC and Intel. See macOS server, Macintosh, operating system and Mojave.

Name Evolution
The Mac originally used "System" designations, which then became "Mac OS." Starting in 1999, Mac OS X was a major upgrade. The Mac OS X moniker was used with a subtitle of an animal name and later a California location (see Mac OS X).

 Intro  Official Name

 1984   (Classic) "System" 1 to 7.5

 1995   (Classic) "Mac OS" 7.5.1 to 9.2.2

 1999   "Mac OS X" 10.0 to 10.8

 2013   "OS X" 10.9 to 10.11

 2016   "macOS" 10.12 and up