Biomass is plant or animal waste that's used as fuel.
Biomass breaks down to bio, or living, and mass, or weight. You can use biomass as a technical term for the total mass of living stuff in a particular area, like the biomass of Kansas, or the biomass of your kid brother's room (yuck). We frequently use biomass to talk about natural material that can be used as fuel, like cow dung, which burns as well as coal.
