My Calibre library of about 50 books currently has no Tags, Category, Genre or Subject fields, as indicated in the left pane in Calibre (where it says "Tags [0]", "Subject [0]" etc.). However when I look at the books in iBooks on my iPhone and sort by Category, I see a number of the books have categories attached, including some very strange ones (like Cannery Row being listed under "French literature"). See pics for details:
I would have thought iBooks categories would be built from Tags/Category/Genre/Subject but it appears they're coming from some (possibly hidden) metadata in the books. Is there a way in Calibre I can view and edit all the metadata in a book, and not just the few fields that are available under the Edit Metadata dialog box?