@Martin Sleziak, a tag 'online-resources' could be a useful one, and I agree with @François Dorais that adding it might be a good idea.
@François Dorais: Concerning the tag geometry, there are about 500 questions with that tag which do not also have a geometry-related tag: mathoverflow.net/questions/tagged/…
That is still a lot, but significantly less than the total of nearly 700 questions tagged geometry.
A correction: In my preceding message, I meant "...there are about 500 questions with that tag which do not also have a geometry-related top-level tag" (the correction is italicized).
