Screenwriters are storytellers whose preferred format is the script.
While many also create beat sheets and outlines to aid with the screenwriting process, they can still get unsettled when asked to write prose—which is exactly what a film treatment is.
A film treatment is the prose telling of the story that takes place in a script.1 It is also written in third person and present tense – just like a script – so it’s not entirely different than the document from which it’s inspired.
Some people may think of a film treatment as a synopsis, but film treatments are generally too long to be considered a synopsis. A synopsis is usually a paragraph or two at most that concisely gives an overview of the script’s story. Even though a film treatment is considerably shorter than the script itself, it typically contains several key plot points and details that could not fit into a shorter synopsis.
Film treatments are also different from film outlines. A film outline is typically meant strictly for the Screenwriter’s eyes (in some cases, the Writer’s Manager or Agent may also see it). An outline can also be significantly longer than a treatment, which often comes in at 10 pages or less. The formatting of an outline also differs from that of a film treatment in that Screenwriters sometimes like to write their outlines as a bulleted list rather than in prose.