Stocking stuffers for brats can include coal, which is a five-letter word. Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata and is mostly composed of carbon. It is widely used as a fuel, primarily for combustion to produce electricity and heat, and is also used in the production of steel and cement. Coal has been used since ancient times as a source of energy and is still an important part of many countries' energy mix today.