Ballistics evidence refers to the study and analysis of firearms, bullets, and the patterns of damage they cause, particularly when a weapon is discharged. It is used in criminal investigations to link projectiles and casings found at a crime scene to a specific weapon or to determine other details of a shooting incident, such as the trajectory or distance from which a shot was fired. Expert ballisticians can match unique markings on a bullet or casing to the specific firearm that fired it, providing critical evidence in firearm-related cases.