(Please note - indeed @Dan Bron came up with the word exposition, which is now used to further clarify the question.)
There are many specific terms for different types of corny exposition in films.
For example a "pull-down-the-map" scene has a specific slang term, "the big board".
Sometimes the "corny exposition" is presented in textual form as a crawl...
Is there a term for using the crawl for corny exposition?
(Of course, a crawl need not be "corny" - in Star Wars the opening is generally well-loved!)