The story board tells the story of the movie, game, TV show etc… in the form of still sketches, renders or photos arranged in order, similar to a comic book. Together with accompanying notes this gives a general idea of how the final piece may look by determining what is in frame i.e. actors and props, what the actors are saying, the passage of time and what the camera is doing in the scene.
Below is the storyboard from the famous shower scene from Hitchcock’s Psycho.
And the scene from the movie (if someone hasn’t seen it before).