macOS Sierra is the thirteenth major release of macOS, Apple Inc.'s desktop and server operating system for Macintosh computers. The name "macOS" stems from the intention to unify the operating system's name with that of iOS, watchOS and tvOS. Sierra is named after the Sierra Nevada mountain range in California and Nevada. Specifically, Lone Pine Peak is the location for macOS Sierra's default wallpaper. 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. From Wikipedia
