A content moderator is supposed to fix up any content such as useless comments, useless/unnecessary edits, etc. They can delete comments, pages, blogs, etc and are able to quickly rollback any edit.
An admin has the same powers as a content moderators, except that they are able to block any misbehaving players.
A bureaucrat has the same powers as an admin, except they can promote other editors to bureaucrat too. Editors can "adopt" wikis if there are no admins/bureaucrats running the wiki. User:Librarian Bird adopted the wiki after the founder became inactive.