There is a tag closed-questions on meta. If you look at the questions, some of them are not about questions which are already closed, but more about process of closing. (E.g., how is question closed, when it can/cannot be closed, etc.)
I would suggest to:
- Create a closing tag on meta.
- Make these two tags synonyms of each other. (Maybe (closing) could be the master tag, since it sounds a bit more general, but I do not have strong preference about the direction of the synonym.)
If there is some agreement that we should have both questions about closed questions and the process of closing questions under the same tag, this should be also added to the tag-excerpt/tag-wiki. And I think that on-hold questions could be included under the same tag.
I will add a comparison with other meta site - the one which I am most familiar with. On Mathematics Meta there are three separate tags closing, closed-questions and on-hold-questions. This sometimes makes users unsure which of the three tags to use.
I have previously asked about possibility of on-hold-questions in MO editors' lounge. Todd Trimble replied that it's better to have them under (closed-questions).