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parallax par·al·lax (pār'ə-lāks')
The apparent displacement of an object caused by a change in the position from which it is viewed.
An apparent shift in the position of an object, such as a star, caused by a change in the observer's position that provides a new line of sight. The parallax of nearby stars caused by observing them from opposite points in Earth's orbit around the Sun is used in estimating the stars' distance from Earth through triangulation.