Origin is Spanish: "tornar" means turning or twisting. A rotating column of air in contact with the ground. It is extending between a convective cloud and the soil. Inside wind speed can reach up to 500 km/h. They can occur anywhere in the world given the right conditions, but are most frequent in the United States in an area bounded by the Rockies on the west and the Appalachians in the east. in the USA it is often called "twister" in Europe we call ist "Trombe", "Wasserhose" if it is above water. The development is yet in research.