1. The vertical movement of energy or mass by circulating currents.
2. The transfer of heat through a fluid by the motion of the fluid itself.

Such motion is usually in the form of currents, in which the hotter, less dense material rises to be replaced below by cooler, denser material.

The transfer of heat caused by the movement of heated material.

In clouds, convection is the up-and-down movement of air caused by heat gradients or areas of different temperatures.