Thermal means relating to heat or caused by heat. When you wear thermal underwear on a cold day, you're wearing specially designed clothing that traps your body heat to keep you warm. A thermal camera detects the heat that objects give off, showing warm things in bright colors and cold things in dark colors. Firefighters use thermal cameras to find people in smoke-filled buildings, and scientists use them to study how animals stay warm.

In science, thermal energy is the energy that comes from the movement of tiny particles called molecules. The faster these particles move, the hotter something feels. When you touch a hot stove, thermal energy transfers from the stove to your hand, which is why it hurts.

You might also hear about thermals in the context of flying. These are columns of rising warm air that birds and glider pilots use to stay aloft without flapping or using engines. Hawks and eagles circle inside thermals, riding the warm air upward like an invisible elevator in the sky. On a hot day, the ground heats the air above it, creating these rising currents that skilled pilots can feel and follow.