Alt text: meme with the ‘Always has been’ format Linux, MacOS, OpenBSD and ChromeOS logos on top of the Earth The first astronaut says ‘Wait, it’s all Unix?’ A Windows logo, on top of the second astronaut. The second astronaut says ‘Always has been’ and points a gun to the first astronaut.
IIRC Mac OS X was changed to OS X before it was changed to macOS. Not that it matters here
Edit: 10.0 to 10.7 were Mac OS X, 10.8 to 10.11 was OS X, 10.12 and later macOS.