A plot or an outline is usually not more than a few sentences long, and defines the genre, the nature and direction of the story.
A story is usually written in prose form, and contains a fair number of chapters with a fair amount of detail, is a few to several pages long, and written in past tense, more like a novel.
A script or a screenplay is a blueprint of the movie being proposed. It is certainly written in present tense, is broken into scenes, and written in three acts. It contains names of characters, descriptions of them and the environment, action, dialogues, details like interior or exterior for the locations.
