A derecho is a widespread, long-lived windstorm that is associated with a band of rapidly moving showers or thunderstorms. Although a derecho can produce destruction similar to that of a tornado, the damage typically occurs 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 miles per hour (93 km/h) or greater along most of its length, then the event may be classified as a derecho.

Derechos are relatively rare in comparison to other thunderstorm phenomena. They occur primarily in the United States, particularly in the Corn Belt region stretching from Texas to the upper Midwest, though they can occur elsewhere, including parts of Canada and Europe. In the United States, there is an average of about one to two derecho events each year, though this can vary widely by location and from year to year.

There are two types of derechos:
1. A progressive derecho is typically associated with a very fast-moving thunderstorm complex that develops along the boundary of hot, humid air to the south and cooler, drier air to the north. These are most common in the summer months.
2. A serial derecho, on the other hand, is produced by lines of thunderstorms that are fueled by the inflow of warm, moist air at low levels from a substantial feed of convective energy. They can be longer-lived and often occur with a bowing line of thunderstorms that appears arched on a radar screen.

The term "derecho" stems from a Spanish word meaning "direct" or "straight ahead," in contrast to the twisting damage path of a tornado. While this might also appear in other contexts in the Spanish language—such as in discussions about legal rights ("derecho" in legal terms means right or law in Spanish) or even used in naming characters in popular media—it has a very specific meteorological definition.

Understanding derechos is important for weather forecasting and for alerting the public about these potentially devastating events. Awareness and preparation can significantly reduce the risks associated with derechos. For instance, securing loose objects, reinforcing structures, and having a reliable means to receive weather alerts can reduce the damage and injuries caused by these powerful storms.