I think they are called movie posters,lol. But as this guide explains, each different size has a different name.

I think this article might answer both of your questions:

http://en.wikipedia.org/wiki/Movie_poster

This made me curious. I can’t remember quite what they were called but I do remember they were called something else. I think they were called billings in old movies because it would have the picture and listing of actors on the posters.