A shotgun, also called a "scattergun", is a firearm designed to shoot a multitude of projectiles with a single pull of the trigger. This makes it very effective at hunting game, greatly increasing the weapon's hit potential. However, the accuracy and power found at close range diminish rapidly as you get farther away from the target. Shotguns designed for military use are often called "combat shotguns".
It's really powerful weapon through much of the game, especially with anyone with high Critical Chance, but it uses far too much ammunition.