The TID number appears at the bottom of the "More About This Book" tab in a Book record. The TID is the unique identifier for the displayed Book Detail page (TID=Title ID). Since the NoveList database has one record per work (Hatchet, for instance) instead of one per edition (hardback, paperback, large print, etc.), we do not use the ISBN as a unique key. Instead, we assign our own unique ID.
Author, Series, and Audiobook Detail pages also have unique identifiers (AID, SID, and ABID).