You remember Venn diagrams, don't you?
Venn diagrams, or set diagrams, show all hypothetically possible relations between a finite collection of elements. They attempt to simplify how various elements in a group are connected to each other. Yeah, school stuff!
They also look really cool... and when they're applied to the world of cinema, they sure make certain movie plots seem at lot more interesting and, well, easy to follow.
Check out a bunch of Venn movie diagrams at Cracked.com. They're educational!