Convection is the movement in a gas or liquid caused by warm fluid rising and cooler fluid sinking. The moving fluid carries heat with it, so the warmth is not sitting still. This is how a room warms above a heater, how soup starts to roll in a pan, how some winds begin, and — on a huge scale — how rock in the Earth's mantle slowly turns over. You meet the word in physics and earth science. Though actually, everyday English stretches it a little: a convection oven is just an oven with a fan that blows hot air around. That fan is not the same thing as warm air rising on its own, but cooks still call it convection because the air is moving and carrying heat. Heat also moves by conduction (through a still object, like a metal pan handle) and by radiation (as rays from the sun or a fire). Convection is the 'the fluid itself is moving' way.