Recently the pc tag wiki was changed to explicitly include Macintosh and Linux as well as Windows. While this is technically correct, I think that in common usage - especially in gamers' terminology - "PC" = "Windows-operated PC", which is distinct from Mac-operated and Linux-operated machines.
For example, the official moto of the Steamplay feature of Steam is
Buy it once. Play it on Mac or PC.
And this is also the image Apple is trying to portray - "PC" as opposed to "Mac". The tag wiki also currently contains a suggestion to tag any pc question with the specific OS in question, so every question about a mac-specific thing should be tagged pc mac, which is probably redundant.
How do we deal with this? One solution might be to revert the tag wiki back and leave it as pc=windows. Another is to remove pc completely, only leaving windows, linux, mac etc. This, in my eyes, is probably the best approach, to avoid ambiguity, but it requires removing one of the most popular tags on the site (well, making it a synonym of windows is probably the correct approach instead of removing it, but you get the idea).