Treatment
A treatment is a prose retelling of a screenplay's full story, written in the present tense and running anywhere from one to a dozen-plus pages. It walks through the plot scene by scene without dialogue or formatting, used to develop, pitch, or sell a story before the script exists.
A treatment tells the whole story in prose: beginning, middle, and end, with the major turns and the emotional throughline, but no scene headings and little or no dialogue. It reads like a short story written in the present tense.
Treatments serve two purposes. As a development tool they let a writer test structure cheaply; as a sales document they let a buyer feel the shape of a film without reading a full draft. Lengths vary from a one-page treatment to a fifteen-page "long treatment."