Definition of: parallax

(par′ə·laks) noun
1. Such difference in the apparent position of an object, specifically a star or other heavenly body, as would appear if it were viewed from two points. It is diurnal or geocentric parallax when due to the change of place of the observer caused by the earth's rotation; annual or heliocentric parallax when the observer's change of place is due to the earth's motion around the sun.
2. Any apparent displacement of an object due to an observer's position. [<MF parallaxe <Gk. parallaxis a change <parallassein alter <para- beside + allassein change]
—par′al·lac′tic (-lak′tik) or ·ti·cal adjective
—par′·al·lac′ti·cal·ly adverb