The Merriam-Webster definition of “depth” that we, as photographic artists, are concerned about is:
2 b: the direct linear measurement from front to back
As I stated in the last article on size, in the world of two-dimensional art, such as drawing and painting, “space” is an art element. In photography, the space is already rendered before the camera, so we look at how size and depth are reproduced, created, and recognized in the photograph.