In order to explain what a tag means, what questions it should be used on and more, tags have tag wikis - this. This tag should be used on questions specifically about tag wikis
A tag wiki is split into 2 parts: the excerpt and the wiki. The excerpt is the shown, plaintext bit that is shown whenever you hover over a tag, or when adding a tag to a question. The wiki, this, is the main meat of the tag that informs you when to use it and what the tag is about. Any user with an account can suggest an edit to a tag wiki, but any user with less than 20000 has to have that edit approved.
This tag should be used on questions about tag wikis, such as suggesting changes to existing wikis, requesting that a specific tag have a wiki written for it or requesting clarifications on an existing tag wiki.