Biomass is mostly processed wood or plant matter. It can also include animal waste products, some household waste and sewage sludge. It comprises renewable organic materials.
The burning of biomass can be considered to be carbon-neutral if the burnt matter is replaced by new planting. The burning process produces CO2, which the newly planted replacements will absorb.
The burning of biomass can be a controversial subject, as some argue that it is not always the case that the burnt matter is replaced, and that in many situations the burning material can cause local pollution. Depending on the source of the biomass, it may also result in damage to forests and biodiversity.
Biomass can also be processed into biofuels, such as methane and ethanol.