Case Lube
Lubricant applied to cases before resizing so the brass slides through the die cleanly instead of sticking and seizing inside it.
Case lube is a thin film of lubricant wiped, sprayed, or rolled onto a case before it is run into a sizing die. Resizing forces the brass through a tight steel ring under considerable pressure, and without lubrication a dry case can stick fast in the die, sometimes tearing the rim off when the press tries to pull it back out.
Lube is essential for full-length sizing with standard steel reloading dies, where the entire case body is worked. After sizing, the residue is removed during cleaning, often in a case tumbling step, so the finished rounds are not slick when loaded.