Biomass is considered any organic material originated from a biological process, spontaneous or provoked, that is usable as an energy source. The origin of these resources can be both agriculture and forestry. Biomass is the way to use organic matter as an energy source.

The organic material from wastewater and sewage sludge is also considered biomass, as well as some municipal solid waste (MSW) and other waste from industries. For biomass to be transformed into heat and electricity, different process can be followed: combustion, anaerobic digestion, gasification and pyrolysis