Organic substances from living organisms that were recently alive, particularly of vegetation, and used as a fuel: Biomass is also especially cultivated for the purpose of fuel or as a source of energy.

Biomass is can be used to produce biofuel that is made from this organic material.

1. The dry weight of living organic matter in a particular ecosystem: The units of biomass are grams of organic matter per square meter.

2. Plant-derived material usable as a renewable energy source: Biomasses can be produced from wood energy crops, such as hybrid poplars and willow trees. Biomasseses can also be obtained from agricultural crops like soybeans and corn, and animal and other wastes.

Biomass is one of the two most common energy sources in the U.S. today, along with hydropower. Forms of biomass, such as wood, can be burned to produce heat and generate electricity.

Agricultural crops can be chemically converted into fuels, such as ethanol and biodiesel. These are the only known renewable liquid energy sources, and may one day replace petroleum and fossil-fuel.

The total mass of living organisms present in a given area. Biomass in the ecology may be specified for a particular species, such as earthworm biomass or for a general category;, such as herbivore biomass.

Estimates also exist for the entire global plant biomass and measurements of biomass can be used to study interactions between organisms, the stability of those interactions, and variations in population numbers.

Whenever dry biomass is measured, the material is dried to remove all water before weighing.