Defined the following convection

Convection is the process of heat transfer in which hotter and therefore less dense matter floats to the top, while cooler and therefore more dense material sinks to the bottom to absorb heat.

Explanation:

Convection is one form of heat transfer; other forms include conduction and (heat) radiation (not exactly the same as the kind uranium emits).

This form of heat transfer is characterised by a use of current in a liquid, in which the sinking and rising create a current which has a shape of a loop.

This requires an outside source of heat, since to sustain the current, once the heated fluid rises up, it must lose heat to the environment to sink, but to rise it must gain heat again.