The term biomass generally really applies to a fuel source rather than a specific generation technology. Biomass fuels are combustible organic materials which can vary dramatically in form. For example, agricultural by products such as wood chips, almond shell, and municipal solid waste are examples of materials which could be combusted with little processing to generate electricity. Cogeneration can utilize biomass fuels, or the material may be combusted directly in a boiler.
Biomass as a fuel source also includes "biogas" fuels. For example, methane recovered from landfills can be combusted to produce electricity. This technology reduces fugitive methane releases (a major greenhouse gas) and produces a useful commodity. Another source of biogas are farms; dairy waste products (manure and other material) can be placed into a "digester" where microbacterial decomposition produces combustible gases. This technique can also be applied at waste water treatment facilities.