The apparent shift of near things against far ones as the viewer moves. Depth revealed by motion rather than by sight alone.
Greek παράλλαξις (parallaxis, alternation), from παραλλάσσειν (parallassein, to change, alternate), from para- (beside) + allos (other); the apparent shift of a thing against its background, named for the changing seen alongside it.
The apparent shift of what is near against what is far as a viewer moves — depth read from motion rather than from sight alone.