Biodiesel: Fuel derived from plant products, such as corn, sugar cane, cellulose (often from grass), vegetable oil, or woody pulp.

The Commons: A resource, such as air or water, that is shared by a large number of individuals and resists sole ownership. Derived from the tragedy of the commons:"the case of a communal pasture area where all individuals are free to graze their livestock. The `tragedy' arises because these `commons' were typically heavily over grazed." ( The principle is easily extended to other environmental resources, which, absent regulation, individuals and businesses have little incentive not to pollute.

Clean Coal: Coal for which efforts have been taken to reduce the emission of pollutants, such as sulfur dioxide and nitrogen oxides. Chemical washing and gasification are two clean coal techniques, while carbon sequestration is a way of limiting greenhouse gas emission from coal. Because coal produces numerous pollutants, and removing any one of them is often only partial, "clean coal" is a relative term.

Ecosystem Services: The multifold ways the natural environment contributes to the human economy. These include air and water purification, agricultural pollination, nutrient cycling, soil enrichment, climate stabilization, medicinal products and drought mitigation; collectively, their global value has been estimated at some $33 trillion a year. See for more information.

Environmental Footprint: The total amount of biological material used, and hence a rough measure of impact on the planet. Ecological footprints may be measured for a person, building, city, nation, or at any of a number of scales. Numerous ways of measuring ecological footprints have been devised.

Environmental Kuznets Curve: The theory that as countries develop they generate large amounts of pollution, but this shrinks as they approach economic maturity. Two major factors thought to cause this shrinkage are increased levels of citizen concern and technological improvements. The EKC is derived from the Kuznets curve, which theorizes a similar tendency regarding economic inequality.

Gandhi, Mohandas Karamchand (Mahatma) (1869 - 1948): Indian leader who used techniques of nonviolence, grounded largely in his Hindu faith, in a campaign that freed India from British rule in 1947.

Globalization: A term used to describe growing interdependence of people around the world with regard to societal influence, economies, and cultural exchanges.

Green Revolution: The new agricultural techniques that, beginning in the 1960s, brought multifold increases in production and greatly decreased the incidence of hunger worldwide. Green revolution techniques include double cropping, pesticide, synthetic fertilizer, irrigation, and crop breeding.

Malthus, Thomas: An English economist who, in 1798, published An Essay on the Principle of Population, warning that while population increased exponentially food production increased only incrementally. Population, he argued, was thus bound to vastly overshoot subsistence, leading to mass poverty and starvation. At least up to the current day, Malthus has proved wrong, as technological advances have allowed food production, along with numerous other goods and services, to advance at an even faster rate than population.

Sustainability: A concept defined by the seminal Brundtland Declaration of 1987: "Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs." Implicit here is the idea that the natural environment faces stress and overexploitation and will not be able to indefinitely meet escalating human demands.

Tonne: A metric ton equal to 1,000 kilograms (A United States ton equals 907 kilograms).

Untouchables: The lowest caste in the hierarchical Hindu system, often called Dalits. While Hinduism recognizes four main castes, said to have come from different parts of the creator god. Thought to have originated from outside of Brahma, untouchables are often isolated from the rest of society and given such menial tasks as handling human corpses and waste. Although the caste system has been officially outlawed by the Indian constitution, in practice many untouchables continue to face discrimination.