Materials that you can burn to create energy.
Coal is a type of black rock, made almost entirely of carbon. It is formed from old plant matter being squashed by the gradual movement of the earth over a very long time. Coal can be burnt, and is often used as the fuel for power plants. Coal is dug out of the ground, from coal mines.
Coal is not the same as charcoal, which is just the black residue after wood is burnt.