Coal
European Commission - Eurostat

International Energy Agency (IEA)
Primary coal is a fossil fuel, usually with the physical appearance of a black or brown rock, consisting of carbonised vegetal matter. The higher the carbon content of a coal, the higher its rank or quality. Coal types are distinguished by their physical and chemical characteristics. These characteristics determine the suitability for various uses. There are three main categories of coal: hard coal, sub-bituminous coal and brown coal (also called lignite). Peat, which is another primary fuel closely related to coal, is often included under coal.

Secondary or derived fuels include solid fuels, liquid and gases produced during coal processing and by coal transformation. They include patent fuels, briquettes (NKB and peat briquettes), gas and coke-oven cokes, gas-works gas and coke-oven gas, blast-furnace gas and basic oxygen steel-furnace gas.

Latin American Energy Organization (OLADE)
This is a black or dark brown solid fuel mineral that essentially contains carbon, as well as small amounts of hydrogen and oxygen, nitrogen, sulfur and other elements. It results from the degradation of the remains of plant organisms during long periods, due to the action of heat, pressure, and other natural physical–chemical phenomena.

Due to the different degrees of change in the process, coal is not a uniform mineral and is classified by ranks according to its degree of degradation, in series that range from lignites and anthracites, which have considerable differences in their volatile contents, fixed carbon and caloric value.

Note: Coal has a very different caloric power before and after washing. In order to avoid inconsistencies, it is advisable to always consider washed coal, that is, without impurities. Coal is known as anthracite, coal, lignite and peat, which are the major varieties and have precise caloric values between 4000 and 8000 Kcal / Kg.

Organisation of Petroleum Exporting Countries (OPEC)
Coal includes all coal, both primary (including hard coal and brown coal) and derived fuels (including patent fuels, coke oven coke, gas coke, BKB, coke oven gas, and blast furnace gas).

United Nations Framework Convention on Climate Change Reporting, Data and Analysis programme
Coal with a quality that allows the production of a coke suitable to support a blast furnace charge and its gross calorific value greater than 23.9 MJ/kg (5,700 kcal/kg) on an ash-free but moist basis and a mean random reflectance of vitrinite of least 0.6.