Solid, liquid or gaseous fuel that is produced from biomass. It is used for generating heat, electricity or in transport. The degree of processing required to use biomass as fuel varies. Solid fuels such as wood chips or straw require minimal processing, while the production of liquid biofuels, for example, requires more complex processes such as fermentation or pyrolysis.

In a narrower sense, biofuel refers to liquid fuels used in transport, bioethanol and biodiesel. They can be used as a full replacement for fuels made from petroleum or blended into them.