The laser pistol sight is a laser beam mounted on your gun that directs a beam in the direction of the aim of the pistol or rifle. If you see the spot from the laser beam, your shot should be at or very near to that spot on the target.
Laser sights may be mounted to the barrel of the gun, or the laser may be mounted in the grip. Grip mounted sights have the advantage that they do not increase the profile of the gun so you can use the same holster or case for a sighted pistol as for an unsighted gun.