A nail gun is a power tool that is used to shoot nails into a target material, instead of having to rely on the swing of a hammer for every nail. These tools are especially useful to roofers because they can drive nails through roofing shingles at a much faster rate without causing the same fatigue and strain as a hammer. Carpenters also frequently use nail guns when they are framing or putting down a subfloor.

Source: The Spruce