According to Steve Kaire, it consists of five elements. All five of these have to be met to get that "slam dunk" project everyone is looking for. The first two are the most difficult and the list is in descending order of importance.
1. Your premise must be original. Not reinventing the whell, but at least an original twist on an old concept.
2. Your story has to have wide audience appeal. This means anyone can think of a new and original concept...original in the author's mind, but the hard part is getting it to appeal to a wide audience.
3. Your pitch has to be story specific. This means that a good pitch will have story specific elements. Maybe not exactly the characters' names, but elements from the story.
4. The potential is obvious. When the potential buyer hears the pitch, he should "see" the basis of the film and know it will work.
5. You pitch should be short. 1 to 3 sentences, 5 max. This is not an act by act rundown; it's an essence of the story thing.
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http://www.hollywoodlitsales.com/cf/journal/dspJournal.cfm?intID=3081