Pa.ral.lax [book]:


  1. The apparent displacement or the difference in apparent direction of an object as seen from two different points not on a straight line with the object.
  2. Astronomy. The apparent angular displacement of a celestial body due to its being observed from the surface instead of from the center of the earth (diurnal parallax or geocentric parallax) or due to its being observed from the earth instead of from the sun (annual parallax or heliocentric parallax). Compare parallactic ellipse.
  3. The difference between the view of an object as seen through the picture-taking lens of a camera and the view as seen through a separate viewfinder.
  4. An apparent change in the position of cross hairs as viewed through a telescope, when the focusing is imperfect.