Storyboard (noun): a sequence of drawings, typically with some directions and dialogue, representing the shots planned for a movie or television production.
This is useful for screenwriters because it shows an intermediary step between screenplays and movies. Any scene, no matter how complicated, can be broken into a series of index card sized key images.
When you’re writing a screenplay, make sure you’re painting a picture. The quality of your prose should create images in the minds eye, images that seamlessly flow into one another.
Owing to this, you can work backwards: all those scene descriptions you’re writing? Make sure each of them literally communicates a specific image.
A great many beginner scripts read like this has never occurred to the author, leading to unphotographable, confusing elements like this:
The battle begins. The orcs ride wolves. They’re led by a gray Mage who kills hundreds with his spell staff. We sense that this is just the tip of the iceberg. The heroes fall back.
Practically, this would be broken into a series of images:
FIRST SHOT: JOHN reacts to the sound of the battle horns. He steels himself, adjusts his helmet. JOHN: It begins. NEW SHOT: Riders crest the hill. At first, they're black dots on the snowy hills. As they charge to the battlements, impossibly fast, we see that they're ORCS, eight foot tall green skinned humanoids mounted on slavering WOLVES. NEW SHOT: John stares at the sight in horror. JOHN: God's wounds. The legends were true... He closes his visor, draws his sword. NEW SHOT: JOHN rides into battle.
The battle, an overhead shot of countless more Orcs dotting the horizon, the gray Mage would all merit one or more shots a piece.
Screenwriting often seems daunting. All the rules, structures, and formatting quirks put people in their heads. If you can use your words to illustrate specific images, you’re already ahead of the game.