1) A movie that is right on the cusp of being taken out of theaters.
2) A terrible or less than enjoyable movie you can view at home.
Both have the same purpose. To create a backdrop to either making out, talking, or a friendly get-together. The former of which is the most common.
"What? In early August? Dude, that is such an Excuse-Movie now. What are you really planning on doing?"
"...possibly getting my hand down her pants..."
"Yeah, have fun with that while Katy Perry is blasting in the background."