The mac-os tag has four questions, all relating to OS X (one is even tagged with both).
Following the lead of Apple.SE, I suggest that the tag (and its synonym macos) be merged into osx.
An alternative would be to use it for questions about Classic (i.e. pre-X) Mac OS, but we already have mac-os-classic for those. Plus such questions are greatly outnumbered by questions about OS X anyway.