How can one tag a whole thread created by someone else?
 

Many threads do not have tags added to them by the original poster.

One can add tags to individual posts within the thread, but how can one just add a tag for the whole thread?

Tagging an individual post will add it to the "Tags used in this thread". We don't have "thread tags" at LQ at this time.

--jeremy

Thanks - I was obviously confused there.