In other words, what cat-egory does it fall under? 
There is a relevant ticket that I just wanted to point out : [BB-403] Works: Type of non-fiction should have more sub-options - MetaBrainz JIRA
I would definitely appreciate a concerted effort from all of us here to come up with a good list of types of works to add to the database, along with a short description for each.
A list was posted of the Bookogs work genres in the following thread, which would certainly need a good clean-up but could be a good starting point: Bookogs genres