The macOS or Mac OS is an operating system that was designed for the Apple Macintosh computer. It was developed by Apple Inc., who also created the Apple I, as well as a number of other more modern products including the iPod, iPhone, and iPad. The main competition to the macOS is the Windows operating system, the most popular OS by a large margin.
Note: The macOS only runs on Apple Desktop and Laptop computers. The iPod, iPhone, and iPad use a different operating system known as iOS.
The first version of the Mac OS, part of the "Classic" Mac OS series, was originally released in the mid-1980s. It did not possess a command line and could only run one application at a time. The first version of the Macintosh operating system to be named "Mac OS" was version 7.6. The most recent version is called Mac OS X or just macOS.