In this thread, I think people are literally thinking of the physical scene--what is in the background? It needs to vary so that the illustrations are not just characters in the same place with different expressions on their faces.
I don't have any famous books handy where I am right now, but I can think of my own experiences:
I recently got a revision request on a picture book that took place at the child's home, the park, and then home again. The editor wanted me to rewrite it so that there was more variation in scene, so I had them do errands on the way to the park.
One of my books (A TEACHER FOR BEAR) takes place pretty much in the same classroom so the illustrator used different angles, different areas of the room, a hallway, etc. to add visual interest.
Another of my books VAMPIRINA BALLERINA has scenes in her bedroom, on the floor of her living room, outside the dance studio, a wide shot of the interior of the dance studio, several smaller shots with different backgrounds, back in her bedroom, the bathroom, a double-page spread cutaway of the castle, a nondescript spot illo where they are sewing, the stage with curtains closed, the stage with curtains opened, a shot of the audience, and I forget what else--all for 380 words.