double-barreled shotgun

A shotgun with 2 parallel barrels either aligned side by side (SxS) or over and under (O/U).

Commonly, they are operated with break-action and usually are sawed off. Early ones have two triggers, allowing firing either one or both shells at once while the later and modern models only have a single trigger capable of firing one and another in quick succession.

In media, they usually wielded in the wild west as coach guns, 18" to 24" barrels, but can also be seen during apocalypses like zombies or wastelands.
In games, Doom II marked it's debut as the Super Shotgun, a more devastating upgrade to the workhorse weapon, the shotgun, and has became a staple in the shooters genre.

This tag implicates shotgun (learn more).