parallax

An apparent shift in the position of two stationary objects relative to each other as viewed by an observer, due to a change in observer position.

[…] Heliocentrick places, to which the Parallaxes being applied, give the Geocentrick.

Planes farther back on the z-axis scroll more slowly than those in front of them, producing a parallax effect. Early games with parallax scrolling tended to have their action taking place all in the forefront plane […]

The angle of seeing of the astronomical unit.

To measure (a distance) based on parallax observations.

To produce an illusion of levels of distance by shifting layers at different rates.