macOS is an operating system designed for the Apple Macintosh computer. It was developed by Apple, who also created the Apple I and 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.
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 macOS, part of the "Classic" macOS 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 "macOS" was version 7.6. The most recent version is called macOS X, or macOS.