The derivatives of macOS are Apple's other operating systems: iOS, iPadOS, watchOS, tvOS, and audioOS.Ī 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. Apple shortened the name to 'OS X' in 2011 and then changed it to 'macOS' in 2016 to align with the branding of Apple's other operating systems, iOS, watchOS, and tvOS.