Convection is basically when a liquid gets hot, rises, cools down, moves to the side and back to the bottom to get hot again. The best example of convection is a pot of boiling water
A more scientific definition of convection is: the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.
hope this helps
