The document discusses biomass as a source of energy. Biomass refers to organic material from living or recently living organisms that can be used to generate heat, liquid or gaseous fuels, and electricity. It can be converted directly through combustion or indirectly by converting it into various forms of biofuel through thermal, chemical, or biochemical methods. Wood is currently the largest biomass energy source. Biomass also includes plant or animal matter that can be converted into fibers or biofuels and can be purposely grown from various plant species.