See also: [2-D design]
A more complete discussion is on the [Volume] page.
In terms of the space that is filled by a 3-D object when viewed
at a distance -- and thus, it will appear as flat 2-D object. The
3-D space tends to mimic the nature of a 2-D drawing, painting, etc.
Of course for the most part the eye is NOT fooled, and "knows"
that there is a 3-D aspect to the object.
Notable exceptions include:
Tension, gravity, etc.
(expand, briefly expound here)
film clip examples, etc.