Use for questions referring specifically to versions of OS X 10.10, Yosemite. Non-version-specific questions related to OS X should be tagged with [osx]. Questions about Mac hardware should be tagged with [mac]. Questions about running OS X on non-Apple hardware are generally considered off-topic.
OS X (pronounced OS ten; "X" is a Roman numeral), version 10.10, codenamed Yosemite, is the 11th major release of Apple's Mac operating system. It was released on October 16, 2014. It is a Unix-based graphical interface operating system.
Yosemite is a 64 bit OS that runs on Intel-based Macs. It includes a major overhaul of the OS X user interface.