Figure/Ground

"Figure-ground refers to the shapes, space or forms within a composition. In simplest terms the figure is what you notice and the ground is everything else."
https://visscom.wordpress.com/2013/04/08/the-principle-of-figure-ground/

Figure-ground is positive and negative space. When I was searching for examples, all of them were two images in one. They all play with space. They are all an optical illusion in a way, where you can look at the image in two ways. At least that's what good figure-ground is supposed to be. 

Here are some examples: