In rifles and handguns, what does the diameter of the bore usually indicate?

The diameter of the bore in rifles and handguns is referred to as the caliber. This measurement is typically expressed in either inches or millimeters and indicates the internal diameter of the firearm's barrel. Understanding caliber is crucial for identifying the appropriate ammunition that the firearm is designed to use, as well as for evaluating the potential performance characteristics of the firearm.

In contrast, other options relate to different aspects of firearms. Gauge pertains to shotguns and refers to the number of lead balls of a certain diameter that equal the weight of one pound. Cartridge is a term that refers to the complete unit of ammunition, including the casing, powder, bullet, and primer, rather than a measurement of the firearm itself. Choke refers to the constriction at the end of a shotgun barrel that affects the spread of shot; it does not apply to the measurement of bore diameter in rifles and handguns. Thus, caliber is the most relevant term for the bore diameter in question.