A storm (from Proto-Germanic *sturmaz "noise, tumult") is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather. It may be marked by strong wind, hail, thunder and/or lightning (a thunderstorm), heavy precipitation (snowstorm, rainstorm), heavy freezing rain (ice storm), strong winds (tropical storm, hurricane, windstorm) or wind transporting some substance through the atmosphere (as in a dust storm, blizzard, sandstorm, etc.).

Storms generally lead to negative impacts to lives and property, such as storm surge, heavy rain or snow (causing flooding or road impassibility), lightning, wildfires, and vertical wind shear which can cause airplane crashes. However, systems with significant rainfall can alleviate drought in places they move through. Heavy snowfall can allow special recreational activities to take place which would not be possible otherwise, such as skiing and snowmobiling.