[hnatt]

Funny thing, "macOS" (actually "мак ос" / "мак ось") was a slang name for OS X in Russian and Ukrainian languages all this time.

[cag_ii]

Weren't all pre OS-X versions also called Mac OS?

[mhurron]

Between versions 7 and 10 it was officially MacOS [VERSION], before that it was referred to as system [VERSION], as in System 6 and so on. That was not an official name, it was the version number of the file `system` and was simply the system that ran on a Mac, because there was only one.

It got the official name MacOS when they allowed the selling of clones.

[wl]

Up until recently, it was Mac OS X.

[umanwizard]

We colloquially call it "Mac OS" in English too.