A recoil pad is a piece of rubber, foam, leather or other soft material usually attached to the buttstock of a rifle

Rifle

A rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile , imparting spin around an axis corresponding to the...

. Recoil pads may also be worn around the shoulder with straps, placing the soft material between the buttstock and shoulder of the person firing the rifle.

The purpose of this device is to provide additional padding between the typically hard buttstock surface and the user's shoulder, to reduce the amount of felt recoil

Recoil

Recoil is the backward momentum of a gun when it is discharged. In technical terms, the recoil caused by the gun exactly balances the forward momentum of the projectile and exhaust gasses, according to Newton's third law...

of the firearm.