The action of placing the hammer or striker under spring tension, making it ready to strike and detonate the primer of a firearm cartridge.
A firearm cartridge is detonated by striking the primer. The mechanism that strikes the primer is a firing pin and a hammer or striker. The hammer or striker is spring-loaded and remains under tension until released by the trigger. To “cock” a firearm is to pull the hammer or striker back against its spring.
Depending on the design of firearm, cocking may be manual or automatic. The majority of modern firearms have double-action triggers, which will automatically cock the hammer or striker before releasing it. An auto-loading firearm will generally be automatically cocked after firing the previous round.