Biomass is all non-fossil organic materials that have an intrinsic chemical energy content.  Unlike fossil fuels, biomass is renewable in the sense that only a short period of time is needed to replace what is used as an energy resource.

Think of biomass as using what you would normally throw away, and then think that instead of being in a landfill, it could be producing hydrogen and methane, straight heat energy, plus made into some sort of compost. Now think of that little Mister Fusion thing in the '80s Back to the Future movies   Biomass - when Doc dumps in those banana peels, coffee grounds, and stale beer to power a vehicle...
Click for Back to the Future site That's the concept of biomass.

Examples of biomass

Forestry crops and harvesting residues

Agricultural crops and harvesting residues

Forestry processing residues

Agricultural crop processing residues

Food processing wastes

Animal wastes

Municipal solid wastes (MSW) and certain other organic wastes

The use of biomass energy has the potential to greatly reduce our greenhouse gas emissions. Biomass generates about the same amount of carbon dioxide as fossil fuels, but every time a new plant grows, carbon dioxide is actually removed from the atmosphere. The net emission of carbon dioxide will be zero as long as plants continue to be replenished for biomass energy purposes. These energy crops, such as fast-growing trees and grasses, are called biomass feedstocks. The use of biomass feedstocks can also help increase profits for the agricultural industry.

Biomass R&D Initiative - US Government site. Biomass offers America a tremendous opportunity to use domestic and sustainable resources to provide its fuel, power, and chemical needs from plants and plant-derived materials. The Office of Energy Efficiency and Renewable Energy Biomass Program includes major programs for developing and improving technology for biomass power; for making biofuels such as ethanol (from biomass residues as well as grain) and renewable diesel; and for making plastics and chemicals from renewable, biobased materials.

Vision for Bioenergy and Biobased Products for the United States

Biomass Discussion Groups

alt.energy.renewable news group - This group discusses topics and issues related to renewable energy.

Alternative Energy mailing list - This DOE forum discusses the current situation and future direction of alternative energy sources.

Bioconversion mailing list - This DOE forum for researchers exchanges information about bioconversion of renewable materials to fuels, chemicals, and polymers.

Bioenergy mailing list - This DOE forum discusses bioenergy issues and projects.

Bioenergy Stoves mailing list - The Bioenergy Stoves mailing list serves as a forum for researchers and others to exchange information, ideas, and opinions about the development of a better stoves for cooking with biomass fuels in developing regions.

Digestion mailing list - This forum discusses anaerobic digestion as a sustainable energy resource.

Gasification mailing list - This forum discusses gasification of biomass as a sustainable energy resource.

IASEE-L mailing list - This e-mail list, maintained by the International Association for Solar Energy Education, serves as a means of communication for people interested in renewable energy education.

sci.energy news group - This group discusses and shares a variety of news concerning energy.