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.
UNIX™ is a trademark name (Think of e.g. IBM AIX, HP-UX, SunOS). Linux and BSD are Unix alike. I believe that Apple has made an effort to be entitled to call an OS of theirs UNIX, not sure whether it’s Darwin or something else.
UNIX is trademarked by ‘The Open Group’, Unix is not. 🙃
To make things more confusing, according to German Wikipedia, Unix is used for Unix-like OSes which are not officially UNIX-certified. 😵💫