Unix is a specific operating system, and there are a lot of operating systems based on it or derived from it (Linux, MacOS, BSD, and both Android and ChromeOS which are based on the linux kernel)

Here's a handy link to the Wikipedia page for unix. You may find the intro & history sections more useful than the stuff about what Unix is from a technical perspective, or how it works.

This may be sacrilege, but I don't mind seeing someone's Windows customizations here, though its not what the community is intended for

Why this guy is getting downvoted for asking a question?

Basically, nowadays Unix (or more formal POSIX) is a standard for operating systems to follow. Most modern operating systems are either derived from Unix (modern MacOS and Solaris), inspired by it (Linux and open-source BSDs) or at least POSIX-compatible (Haiku). Windows is neither of this - being monopoly they basically don't need to follow a standard when they can force everyone to implement their solution.

So yeah, Unix is an OS and Windows doesn't count.

Unix is an operating system and there are a lot of other operating systems derived from it. Windows is one of the few operating systems that are not derived from Unix, although I suppose it would count if you setup WSL and riced it since it runs the Linux kernel.