Definition: An upright wall within the hull of a ship. Particularly a watertight, load-bearing wall.
Hitting your head up against the bulkhead with ex-employees still showing up in Sharepoint?
Check out:
http://sharepointrelated.com/2012/10/11/remove-bulk-users-from-user-information-list-people-picker/
Leave a comment if you have any useful links on bulkhead removers. If you don't know of any, keep looking. They're out there somewhere.