Heat is a form of energy that flows from warmer things to cooler things and makes objects feel hot. When you hold a mug of hot chocolate, heat moves from the mug into your hands, warming them. When you touch a cold doorknob in winter, heat flows from your warm hand into the cold metal, making your hand feel chilly.

Heat is related to the movement of tiny particles called molecules. The faster molecules move and vibrate, the more thermal energy an object has. A pot of boiling water has molecules moving so quickly that some escape as steam. A frozen lake has molecules moving so slowly they lock into place as ice.

We measure temperature with thermometers, but heat and temperature are not quite the same thing. Temperature tells us how hot something is, while heat tells us how much thermal energy it contains. A cup of boiling water and a swimming pool at room temperature might surprise you: the pool actually contains more total heat because it has so much more water, even though the cup feels hotter.

As a verb, heat means to make something warmer. The word also describes hot weather (the summer heat), pressure or stress (the heat of competition), or intensity (in the heat of the moment). When a coach tells players to “turn up the heat,” they mean to play harder and create more pressure.