Just contact the USC Film Program and ask what they want in the outline. You're entering the program to learn, they don't expect you to know all the answers before you enter.
In a properly formatted script, one page is roughly one minute of screen time. In my experience, this is true when you have scripts over 20 pages. A four minute short is likely to run 4-6 pages.
A synopsis is basically your whole story told in one page. A treatment is basically the script without the dialogue. These DO NOT include shooting information. I am guessing that USC is interested in an outline of your story that includes how you would visualize the shots, more like a written storyboard.
As for your story, you can develop that in six pages using a simple model. Everyone here has different techniques which work for them. Some use index cards, others just start writing. My advice is that film tells a story. So rather than worrying immediately about characters and description, write a one page version of your story. Getting the idea onto paper (or computer) is the first step. At this point, I would break it up into the "6 Act Model". Put a header on six index cards or sheets of paper. What I'm going to talk about can be found at Michael Hauge's site:
http://www.screenplaymastery.com/structure.htm
Act 1 - Set Up (introduce the characters and situation)
Act 2 - Introduce a New Situation and a Complication
Act 3 - Formulate a Plan of Action to Succeed (character throws self in headlong)
Act 4 - More Complications and Higher Stakes (usually a major setback)
Act 5 - Final Push to Succeed with it looking unlikely (suspenseful moment, climax)
Act 6 - Resolution and the Ever After
I would go through and put the elements of my story above onto the index cards under the headings. Now I can go back and add details and think about dialogue. The structure of the film is in place. You have six pages that you can then condense down if needed.
But if you really want to know what USC wants, contact them. Why play guessing games or set yourself up for disappointment?