Answer: A parallax error is an apparent shift in an object's position as it is viewed from different angles. For example, the error is most easily noticed by looking at a nearby object with one eye closed, then looking at it through the other eye.
Explanation: Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects show a larger parallax than farther objects when observed from different positions, so parallax can be used to determine distances.