Depth Perception
Depth perception (AKA binocular vision, stereo vision and stereo-acuteness) means the ability to see correctly in 3-D (three dimensions). In other words, when you look at an object or scene you are able to perceive width, height and depth.
Most people have good depth perception but around 10-15% of the population may have some problem, ranging from mild difficulty to complete stereo-blindness (AKA monocular vision). Because perfect depth perception is not essential, however, many people go their entire lives without realising they have a problem.