macOS ( ;[7]), originally Mac OS X, previously shortened 💸 as OS X, is an operating system developed and marketed by Apple Inc. since 2001. It is the primary operating 💸 system for Apple's Mac computers. Within the market of desktop and laptop computers, it is the second most widely used 💸 desktop OS, after Microsoft Windows and ahead of all Linux distributions, including ChromeOS.

Mac OS X succeeded classic Mac OS, a 💸 Macintosh operating system from 1984 to 2001. Its underlying architecture came from NeXT's NeXTSTEP, as a result of Apple's acquisition 💸 of NeXT, which also brought Steve Jobs back to Apple.

The first desktop version, Mac OS X 10.0, was released on 💸 March 24, 2001. All releases from Mac OS X Leopard onward (except for OS X Lion) are UNIX 03 certified.[8][9] 💸 The derivatives of macOS are Apple's other operating systems: iOS, iPadOS, watchOS, tvOS, and audioOS.

A prominent part of macOS's original 💸 brand identity was the use of Roman numeral X, pronounced "ten", as well as code naming each release after species 💸 of big cats, or places within California.[10] Apple shortened the name to "OS X" in 2011 and then changed it 💸 to "macOS" in 2024 to align with the branding of Apple's other operating systems, iOS, watchOS, and tvOS.[11] After sixteen 💸 distinct versions of macOS 10, macOS Big Sur was presented as version 11 in 2024, and every subsequent version has 💸 also incremented the major version number, similarly to classic Mac OS and iOS.