A tornado is a rotating column of air in contact with the Earth and cumulonimbus clouds, primarily caused by weather instability and wind shear. Tornadoes can vary in intensity, with most classified as weak (EF0 or EF1) and causing significant destruction, injuries, and fatalities, especially in the U.S. where they occur frequently in 'Tornado Alley.' Precautions to ensure safety during a tornado include knowing warning signals, seeking shelter, and having a family communication plan.