Mechanical, optical, or electronic devices used to aim a gun.
The mechanical parts on the top of the barrel that allow you to aim the gun. There is a front sight which is usually a post on the top of the muzzle, and a rear sight which has a notch in it. The rear sight may be an adjustable device on the breech end of the barrel or just a groove cut into the top of the breech end of the barrel.
Front and rear components used to align a firearm with its intended target.