Depth is the . apparent distance from front to back in a piece of artwork.
b. distance or area between, around, above, below, and within objects.
c. degree to which the surface of an object seems to have a particular feel.
d. area of dark created when an object blocks light

depth is the:

a. Appartent distance from front to back in a piece of art work.

Explanation:

The depth refers to the deep part of something or that is extended throughout.

In art, depth can only be given by the use of defined techniques and proportions of light or the lines that give the opposite sensation or thought to stiffness.

Now, if the person is seeing a painting that has depth, he will observe it from front to back or the opposite. Since it is a defined area within a plane.