Zeroing a red dot sight is the process of aligning the reticle of the sight with the point of impact of the bullet. This is important to ensure that the sight is accurate and that the shooter can hit their target. There are a few different ways to zero a red dot sight, but the most common method is to use a boresighter.
A boresighter is a laser device that is inserted into the barrel of the gun. The laser beam will project a dot onto the target, which can then be used to align the reticle of the sight. Once the sight is aligned, the shooter can fire a few rounds to confirm that the sight is accurate.