Stuff on a DVD that isn't the movie, e.g. a
CommentaryTrack. To some
MovieNuts,
SpecialFeatures are as important as, or more important than, the movie itself. Buying a DVD for the special features even if you don't particularly care for the movie is positive proof that you're a
MovieNut.
Perhaps more telling is buying a DVD for the special features when you already own a copy of the movie on DVD...