A treatment is basically the screenplay written in a sparse, short story format, condensed to one page. This can also be referred to as the synopsis or pitch, but is a separate thing from “scriptment” which would be a treatment of between twenty and thirty pages long.

A pitch is actually usually the verbal presentation of the script to the recipient (production company, agency, etc)…

A synopsis sums up the screenplay. It is usually composed of all of the beats of the screenplay plus the conclusion.

A summary would not necessarily contain all beats. It could be as short as a sentence or paragraph.

If someone requests a summary or synopsis, you need to find out how long a document they want; that will tell you how complete or detailed you should be.

In short, Treatment is a blow-by-blow synopsis of your script. Anywhere from 3-40 pages, depending on the detail desired. Can be more like an outline, or it may detail every action in the script (just omitting dialogue.)

A synopsis or summary is a general view, or a collection of heads or parts so arranged as to exhibit a general view of the whole; an abstract of a discourse; a syllabus; a conspectus.