Cheek piece, cheek weld. What else do you call it?
The cheekpiece is part of the stock. Cheek weld is how your cheek rides on the stock--how hard it mashes on there, whether a bunch of your cheek moves up toward your eye socket, etc. A consistent cheek weld is one of the keys of hitting stuff regularly and shooting small groups. You probably do it that way already without knowing the name for it.
Okie John