High Sierra Definition High Sierra is the common name of macOS 10.13. It is the 14th version of Apple's desktop operating system, and follows Sierra, macOS 10.12. Apple released macOS High Sierra on September 25, 2017. The similarity of the name "High Sierra" to "Sierra" is not coincidental, as it was designed to be a performance update rather than major feature update. Previous performance updates include Snow Leopard (which followed Leopard), Mountain Lion (which followed Lion), and El...