In terms of optics, what does parallax error refer to?

Parallax error specifically refers to the phenomenon where the position of the reticle (the crosshairs or aiming point in a scope) appears to shift in relation to the target when viewed from different angles. This misalignment occurs because the reticle and the target are not in the same plane, causing a discrepancy in alignment. When the shooter is not positioned directly behind the scope, the perceived position of the target can change, leading to potential inaccuracies in aiming.

This understanding of parallax error is essential, particularly for precision shooting and using optical sights, as it highlights the importance of proper eye alignment and positioning. If a scope has parallax error and the shooter does not account for it, this can result in missed shots or inaccuracies, especially at varying distances.