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