From 10.0 through 10.8, releases of Mac OS X were named after big cats: for example, Mac OS X 10.6 is usually referred to by Apple and users as ' Snow Leopard'. The first version released was Mac OS X Server 1.0 on March 16, 1999, and a desktop-oriented version, Mac OS X 10.0.0 'Cheetah' followed on March 24, 2001.

From its sixth release Mac OS X 10.5.0 'Leopard' onwards, every release of Mac OS X for Intel processors gained UNIX 03 certification. Mac OS X (whose X is the Roman numeral for 10 and is a prominent part of its brand identity) is a Unix-based graphical operating system, built on technologies developed at NeXT (from the second half of the 1980s to Apple's purchase of the company in late 1996) in combination with technologies from Apple's 'classic' OS and technologies from FreeBSD. OS X was rebranded macOS by Apple in 2016. It is the successor to Mac OS 9, the final release of the 'classic' Mac OS, which had been Apple's primary operating system since 1984. Since 2002, Mac OS X has been included with all new Macintosh computer systems. OS X (pronounced oh ess ten) is the brand name of a series of Unix-compatible operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc.

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