What’s the difference: spec script, treatment, pitch and outline?
These terms deal with different forms or stages of a screenwriter’s work. A "spec script" is a completed screenplay, probably about 120 pages long, that a writer wrote on his own. That’s the "spec" part, meaning that no one paid the writer in advance to write it, just like a house built on spec doesn’t have a buyer until it’s finished. Most writers’ first screenplays would be considered specs, because it’s rare for someone to hire a writer without reading his or her work first.
"Treatment" and "outline" mean different things to different people, and one writer’s treatment might be another’s outline. Regardless, treatments and outlines map out a movie story, often as a precursor to writing the full screenplay. An outline might be one page or might be ten; a treatment could be three pages or could be thirty. James Cameron is known for writing "scriptments" that are 70 pages or more. Ultimately, the length is less important than the function: hopefully, an outline or treatment will help a writer spot problems early on, so that the finished script will be better. Treatments are usually written in paragraph rather than screenplay form, but there are no hard and fast rules. Outlines are often more rudimentary, with just sluglines to refer to sequences.
A "pitch" is the oral presentation of a movie idea, where screenwriters explain to studio executives that their movie is "Ghostbusters meets Titanic." God knows why screenwriters – who spend most of their days typing in dark rooms – are supposed to be able to suddenly become eloquent and impassioned hucksters, but such are the weird realities of Hollywood. Ideally, a pitch should feel like how you describe a really good movie to a friend who hasn’t seen it yet. Casual but excited. Truthfully, I usually write every word I’m going to say ahead of time, then internalize it so it feels like I’m ad-libbing. There might be situations when you give a "written pitch," but truthfully, that document would probably be an outline or treatment.
I’ve been on panels dedicated to the topic of pitching, and I’ve come to the conclusion that it’s not a skill that can really be taught. It’s like stand-up comedy. You have to learn through practice in front of actual human beings.