But what do they mean by that phrase then? I think a lot of people who think "macOS isn't Unix" (or similarly, "z/OS isn't Unix") aren't aware of the legal sta

But what do they mean by that phrase then? I think a lot of people who think "macOS isn't Unix" (or similarly, "z/OS isn't Unix") aren't aware of the legal status of the term "Unix" – that it is a registered trademark owned by The Open Group, and legally a trademark means whatever the trademark owner says it means – and The Open Group is very clear that "Unix" means any system, irrespective of its marketing or heritage or other functions, which passes their test suites and whose vendor pays the licensing fee.