Convection is the circular motion that happens when warmer air or liquid — which has faster moving molecules, making it less dense — rises, while the cooler air or liquid drops down.
Convection is a major factor in weather. The sun heats the earth’s surface, then, when cooler air comes into contact with it, the air warms and rises, creating an upward current in the atmosphere. That current can result in wind, clouds, or other weather. Convection currents within the earth move layers of magma, and convection in the ocean creates currents. Convection ovens use fans to circulate heat so that whatever you're cooking cooks faster and more evenly.