What type of storm is a "derecho"?

When most people think about winds associated with a thunderstorm, they think of tornadoes; however, most years there are far more damage reports from thunderstorm straight-line winds than from tornadoes. Straight-line winds are thunderstorm winds that have no rotation, i.e. not a tornado. A derecho (pronounced similar to "deh-REY-cho") is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms. Although a derecho can produce destruction similar to the strength of tornadoes, the damage typically is directed in one direction along a relatively straight swath. As a result, the term "straight-line wind damage" sometimes is used to describe derecho damage. By definition, if the wind damage swath extends more than 240 miles (about 400 kilometers) and includes wind gusts of at least 58 mph (93 km/h) or greater along most of its length, then the event may be classified as a derecho.

Source: National Weather Service