A 12-gauge is a type of shotgun that uses a specific size of ammunition, known as a gauge. The term "gauge" refers to the diameter of the shotgun barrel, with a 12-gauge being approximately 0.729 inches wide. This size is popular for various uses, including hunting, sport shooting, and home defense due to its versatility and effectiveness. The 12-gauge shotgun can fire different types of shells, such as birdshot, buckshot, and slugs, allowing it to be adapted for different shooting scenarios. Its widespread availability and range of ammunition options make it a common choice among shooters and hunters.