Biomass is, together with the wind, the natural fuel for excellence, existing in nature in an ongoing and diversified manner . Under this name there are grouped different types of materials of organic origin, animal or plant-fossil, which, properly treated, can become solid, liquid or gaseous.

Biomasses are therefore, in addition to the essences grown specifically for energy purposes, all products from agricultural crops and forests, including residues from the working agricultural and forestry, food waste and agricultural products intended for human or animals,the residues, not chemically treated, the wood processing industry and paper, basically all organic products coming from biological activities by animals and humans.