However, we have a few tags at meta which have no question. A few examples: vote-to-close, votes, login, data-dump, interesting-tags. (Situation might change later, but you can find out whether we have such tags simply displaying tags by popularity and going to the last page.)
These tags are empty but they do exist in the system in the sense that they are between suggestions when you tag a question, you are also offered a possibility to create a wiki, when you display the tag, etc. Compare with a tag that really does not exist: abcdefgh.
Here are screenshots (as of June 24, 2012):
So I was curious whether empty tags are pruned at meta, not only at main. And if they are, how often does this happen?
EDIT: I guess this question might be more appropriate for meta.SO, so perhaps in a few days I'll try to search meta.SO once again and if I don't find anything related to this there, I'll ask there. (One of the reasons I've posted the questions here was that I was not able to find examples of such tags at meta.SO.)