The term "relative size" refers to the depth cue in which we perceive distance based on the comparison of sizes between objects. It is the idea that when two or more objects are similar, we assume that the smaller one is farther away.
Related terms
Interposition: Interposition is a depth cue where one object partially obstructs our view of another object, leading us to perceive it as closer.
Linear Perspective: Linear perspective involves perceiving parallel lines converging at a point in the distance, indicating depth and distance.
Texture Gradient: Texture gradient refers to the gradual change in texture as objects recede into the distance, providing a depth cue.