Carbon offsets: The opportunity to defray production of CO2 (carbon dioxide) by rewarding or subsidizing someone else's carbon-saving behavior. For example, a company might plant a certain number of trees to make up for the CO2 it produces through other activities.

Clean energy: Energy from renewable sources such as biomass, wind or solar power. Hydropower also can be called clean energy because it, too, has zero emissions, but often, today's hydropower still has substantial impacts on aquatic ecosystems. Waste-burning and wood-burning plants that capture emissions can be clean-energy generators. Fossil fuels do not meet the criteria of clean energy because of their emissions and environmental impacts.

Climate change: Short and long-term effects on the Earth's climate as a result of human activities such as fossil-fuel combustion and vegetation clearing and burning.

Compact fluorescent: A scaled-down version of standard fluorescent lamps which are used to replace standard incandescent lights. These bulbs consist of a gas-filled tube and a magnetic or electronic ballast.

CFL: Compact fluorescent lamp, also known as a compact fluorescent light bulb.They last 10 times longer and use about one-quarter the energy of incandescent bulbs. But because they contain a small amount of mercury, they have to be disposed of properly and should never be broken.

Composting: The process of degrading organic material by microorganisms in aerobic conditions.

Conventional power: The generation of power from sources such as petroleum, natural gas or coal. Large-scale hydropower and nuclear power often are considered conventional power sources.

E85: A fuel that is 85 percent ethanol (vegetable-derived alcohol) and 15 percent gasoline.

Emission(s): A substance(s) or pollutant emitted as a result of a process.

Energy: The capability of doing work; different forms of energy can be converted to other forms, but the total amount of energy remains the same.

Energy audit: A study of a home, building or facility to determine energy consumption and ways to use less energy.

Energy Efficiency Ratio (EER): The measure of the instantaneous energy efficiency of room air conditioners; the cooling capacity in Btu's per hour divided by the watts of power consumed at a specific outdoor temperature (usually 95 degrees Fahrenheit).