Final answer:
The term 'gun being locked in battery' refers to a firearm's action being fully closed and ready to fire, with all components properly aligned for safe and correct discharge. This is a mechanical status relevant for the safe operation of semi-automatic firearms.
Step-by-step explanation:
When referring to a gun being locked in battery, it means that the gun's action is fully closed and ready to fire. In this state, the breech is closed, and the firing pin, bullet, and primer are properly aligned. This term is especially pertinent in semi-automatic firearms where the mechanism must be in battery for the gun to fire safely and correctly. Firearms have mechanisms to prevent firing when not 'in battery' to avoid dangerous situations. The term may also sometimes be used in the context of firearms safety regulations, although not directly related to its mechanical meaning.