About OS X
OS X is a Unix-based operating system created and sold by Apple Inc. for their Macintosh computers. It first debuted in 1999 with Mac OS X Server 1.0. It is based off of NeXTSTEP, NeXT's operating system, which in turn is based off of the Mach kernel. The X in OS X is the Roman numeral for ten and such, pronounced as ten and not as a normal "x".
How to use the tag
This tag is for any and all questions related to OS X. Questions about the hardware should be tagged mac instead.
It is against the Mac OS X EULA to install OS X on any non-Apple branded hardware ("Hackintosh"). Hackintosh questions are considered off-topic for Super User.
There are several related tags for osx designed to specify the version of OS X in use such as:
osx-yosemite – OS X 10.10 (Yosemite), the latest public version, adding Handoff, iPhone calls, SMS, Instant Hotspot, and a new dark theme.
osx-mavericks – OS X 10.9 (Mavericks), adding iBooks and Maps, and focusing on power-users such as better multi-display support.
osx-mountain-lion – OS X 10.8 (Mountain Lion), adding Notification Center, Reminders and Notes.
osx-lion – OS X 10.7 (Lion), which included new features such as full disk encryption, Mission Control, Auto-resuming apps and additional support for multi-touch gestures.
osx-snow-leopard – OS X 10.6 (Snow Leopard), an upgrade that primarily focused on speed and stability.
osx-leopard – OS X 10.5 (Leopard), which introduced many new features such as a redesigned Finder, the "Spaces" desktop management and the Time Machine backup utility.
osx-tiger – OS X 10.4 (Tiger), which introduced the Spotlight search, the Automator scripting tool and Dictionary.
osx-panther – OS X 10.3 (Panther), which updated Finder and introduced Exposé, the File Vault encryption and the Safari browser.
osx-server – a specialized server version for OS X which used to be released along with the "normal" OS X versions. As of 10.7 Lion, OS X server additions can be installed as an application package through the Mac App Store.
Questions about OS X can also be asked on Ask Different, which is focused on Apple products.