What does "parallax error" indicate in optics?

Parallax error in optics refers specifically to a perceived shift in the target's position that occurs when the shooter's eye is not perfectly aligned with the optical axis of the sight or scope. This misalignment results in an apparent movement of the target relative to the reticle, leading to inaccuracies in aiming.

When parallax error is present, the shooter may see the reticle in a different position against the target depending on their line of sight. This can be particularly problematic at varying distances, as the degree of parallax can change based on the distance to the target and the scope's design. Correctly aligning the eye with the scope helps minimize parallax error and ensures a more accurate shot.

Other options may describe different phenomena in optics and shooting but do not accurately define parallax error, which is specifically tied to eye positioning relative to the sighting device.