A "12 gauge" refers to a specific size of shotgun, which is a type of firearm designed to shoot shells filled with pellets or slugs. The term "gauge" indicates the diameter of the shotgun barrel; in this case, a 12 gauge has a larger diameter than smaller gauges like 20 gauge. This size is popular for various uses, including hunting, sport shooting, and home defense. The 12 gauge shotgun is versatile and can fire a wide range of ammunition types, such as birdshot, buckshot, and slugs. Its effectiveness and power make it a common choice among hunters and law enforcement. Additionally, shotgun shells for 12 gauge firearms are widely available, contributing to its popularity.