(4) Biomass most often refersto plants or plant-based materialsthat are not used forfood or feed, but as energysource. Biomass fuels comefrom things that once lived:wood products, dried vegetation,crop residues, aquaticplants and even garbage. It isknown as 'Natural Material'. As an energy source, biomasscan either be used directly viacombustion to produce heat,or indirectly after converting itto various forms of biofuel.