From Anyone Can Create an App by Wendy L. Wise

Storyboards are a little bit like what they sound like – a way to visualize a story and how the parts of the story are related. If you imagine a graphic novel (I’ve heard that’s what the cool kids are calling comic books these days), there are multiple panes that tell a story. Each pane flows into the next so the reader can follow the story. Imagine if you were writing your own graphic novel – you could start out with several blank panes and lay them out so you could begin planning the novel. You might sketch in a few details on each pane to start, and then you might begin filling in more details as time progresses.