Coal is a mineral, a black rock that can be extracted from the earth and burned for fuel. Most of the electricity that's produced in the world is powered by the burning of coal.
Coal may seem like an old-fashioned fuel, making you think of steam locomotives that ran on coal, or coal fires heating homes in the nineteenth century. Some people still burn coal in stoves today, although most coal is burned on a much larger scale, generating electricity for entire towns and cities. You can also use the noun coal to mean a glowing ember in your fireplace or backyard grill. In Old English, it was col, from a Germanic root.