"Windows" actually is related to what it does. As you might already know, before Windows, you just had DOS, which was 100% full screen all the time. Then Windows came along an let you run DOS programs (and Windows programs, of course) inside of their own windows, and let you have multiple windows open at once. Then, only after that was hugely successful, it became its own standalone OS. So at least at the time it was created and became popular, its name was very related to what it did.