Biomass is the term for substances, which have grown from animal or vegetable matter.
It is relevant to the renewable energy sector, because energy from biomass fuels is renewable, unlike fossil fuels. This is because the biomass absorbs as much CO₂ when growing as it releases when it is converted to energy.

Biomass fuels and conversion to energy

Biomass is derived from plant material and animal wastes. It can be used to generate electricity and or heat and to produce transport fuel.

A very wide range of biomass can be used for energy purposes. Examples include agricultural wastes, eg straw and other crop residues; crops grown specifically for energy production, eg willow, miscanthus, oil seed rape and wastes from a range of sources including food production. The nature of the fuel will determine the way that energy can best be recovered from it.

There are a huge number of different biomass fuels, most of which come from agriculture and forestry.
Biomass comes both in its natural state (we call this primary biomass), and also after processing or being used for other purposes first. For example sawdust, straw and used paper are biomass sources, which can be used for fuel.