A tornado is a tube of violently spinning air that touches the ground. Wind inside the tornado spins fast, but the actual 'circle' of wind around them is huge. This makes tornadoes very dangerous. Tornadoes are especially dangerous to people in cars, trucks, buses or mobile homes and about 60 people are killed by tornadoes every year. The word "tornado" might come from the Spanish word tronada (thunderstorm), which comes from the word tronar (to thunder).