What is a screenplay?
A script for a film including dialogue and descriptions of characters and sets.
Screenwriting is the art and craft of writing scripts for film, television or video games.
Novel Vs. Screenplay
A novel is driven by action which takes place inside the character's head, and is often called the mindscape of dramatic action.
In screenplays, the character’s inner lives can only be shown through their actions, never their thoughts.
In a screenplay all the action is written in present tense. The reader follows the action as it happens. Everything is written exactly as it will appear on the screen. Nothing that cannot be seen is written.
Dialogue in a novel tends to be how we imagine conversations in our head.
Screenplay dialogue is designed so the words fit the pacing and tone of the script and come out of the mouth much easier than dialogue in a book would.