The macOS Sierra developer preview: Different name, same ol’ Mac
When Apple runs through its operating system announcements at WWDC, the OS X part of the show is pretty much the only instance when the company spends any time talking about a product name.
The Mac has long since ceased to be Apple's most important product, but the company has kept up the tradition of slapping a secondary name on each OS release, something separate from the version number and the "OS X" or "Mac OS X" branding. Often, those names are used to set expectations about the release. Snow Leopard is a refinement of Leopard. Mountain Lion is a refinement of Lion. El Capitan is a refinement of Yosemite.
