Out-of-battery refers to the status of a firearm before the action has returned to the normal firing position.
In firearms and artillery where there is an automatic loading mechanism, a condition can occur in which a live round is at least partially in the firing chamber and capable of being fired, but is not properly secured by the operating mechanism, known as the bolt in handheld firearms, of that particular weapon.
The gas pressure produced at the moment of firing can rupture the not fully supported cartridge case and can result in flame and high-pressure gas being vented at the breech of the weapon, potentially creating flying fragments and possibly injuring the operator.
Operator injuries from out-of-battery discharges often include cuts and velocity wounds to the hands, arms, and face.
Depending on the design, it is also possible for a semi-automatic handgun to simply not fire upon pulling the trigger when in an out-of-battery state.