Mac OS is an operating system like Windows and Linux on Mac computers that began in 1984 by Apple, although more expensive than the regular Windows PC. Today, Apple's Mac is still more expensive than Windows.
The current version is Mac OS X Sierra 10.12.
The Macintosh OS originated on the first Apple Computer, the Apple Macintosh. It preforms the same functions as Windows but doesn't has a library as vast as Windows and is therefore best suited for business and school use. It doesn't have many games for its platform but is desired for certain programs like Garage Band and some editing software. The Macintosh was named after Steve Jobs' favorite type of apple, the McIntosh Apple.
Mac OS has a tool called Boot Camp that allows you to install Windows on a Macintosh, this is due to how Apple originally designed the PC on MS-DOS, which in the final versions of Macintosh, was changed entirely, making it a standalone PC.
Only a few pieces of malware that targets the Mac OS, as it has a low market share.