Find Orphan Taxonomy Terms - Drupal 6
Please make sure you have 'Views' and 'Term Node Count' modules are installed.
Deleting orphan terms especially in a free tagging vocabulary is reasonably common task for site administrators. Orphan terms in this case means taxonomy terms that are not used by any nodes (content pieces). I had to look up various issue queues for this and found this in the issue queue of the term node count module. If interested here is the link to the page #603868: Rework Term Node Count for D7
Steps to get this working:
There you have it a view bulk operation page that allows you to delete the orphan taxonomy terms easily. You can delete all terms in one fell swoop. For better security choose the access setting and change to a higher role or permission so that unwanted users don't delete the terms. You can easily add this link to a menu and do the delete operations at your leisure. Mind you if you are using a hierarchial vocabulary it is probably best to keep a way to remove the top level terms from the list so that the tree remains intact. However I havent found a way of getting that done.
Please make sure you have 'Views' and 'Term Node Count' modules are installed.