macOS - Wikipedia
macOS (/ˌmækoʊˈɛs/; previously Mac OS X and later OS X) is a series of proprietary graphical operating systems developed and marketed by Apple Inc. since 2001.
OS X 10.11: El Capitan (Gala) - 30 September 2015 - Macworld UK
Every version of Mac OS X and macOS ever from the first to the latest macOS, plus how to tell which version you have. Mac OS X was first introduced almost 20 years ago in September 2000.
List of Mac OS versions | Apple Wiki | Fandom
Note: The headings on this list indicate the Macintosh System bundle names; the bullet points indicate the version of the System File included in that bundle. This is to make it clearer for people searching for specific bundle versions as opposed to System File versions. Finder File versions are not indicated.