The word biomass is derived from the Greek term “bios”, meaning “life”. Broadly speaking, therefore, biomass refers to all living organisms, including the organic matter left behind after death. A uniform definition of the term has thus far not been established. In the context of renewable energies, biomass refers to all plant or animal matter that can be used as an energy source. Examples of such matter include wood, straw, grasses, cereals, and plants containing sugar and oil, as well as human and animal excrement, organic waste (household, commercial or industrial), and paper. Fossil fuels such as lignite, oil and natural gas (originating in prehistory) do not fall under this category, despite having been formed from decomposed plants and animals.
Saskia Blank of the Ideas 2020 team answered this question.