macOS Sierra (version 10.12) is the thirteenth major release of macOS (previously Mac OS X from 2001 to 2012 and OS X from 2012 to 2016), Apple Inc.’s desktop and server operating system for Macintosh. It was the first version of the operating system issued under the June 2016 rebranding as macOS. Sierra is named after the Sierra Nevada mountain range in California and Nevada. Its major new features concern Continuity, iCloud, and windowing, as well as support for Apple Pay and Siri.
The first beta of macOS Sierra was released to developers shortly following the 2016 WWDC keynote on June 13, 2016. The first public-beta release followed on July 7, 2016. It was released to end users on September 20, 2016, as a free upgrade through the Mac App Store and it was succeeded by macOS High Sierra on September 25, 2017.