Burnish
Definition: To make smooth or glossy by rubbing; polish. To rub with a tool that serves especially to smooth or polish. To improve or make more impressive.
Purpose: To make the crease more flat, so a card will lay closed.
Do you ever want to get a nice crease in a piece of cardstock? If so, you can “burnish” the end using a Bone Folder to get the nice polished finished crease.