Head Stamp
The markings on the base of a cartridge case identifying maker, caliber, and sometimes year. The first thing to check when sorting brass.
Head stamps tell you cartridge family (LR for Long Rifle, WIN for Winchester, FED for Federal, LAPUA for Lapua, etc.), the cartridge name, and sometimes a lot or year code. Military cases often add NATO markings.
Reloaders sort brass by head stamp because case capacity varies subtly between manufacturers. Mixing Lapua and Hornady brass in the same load string can blur your ES data. It pays to keep each batch consistent so your numbers mean something.