RENEWABLE ENERGY: Energy derived from renewable sources such as wind, solar, geothermal or plant matter. This type of energy is growing fast in the U.S., but it remains a small contributor to the nation's energy mix. Ten percent of U.S. gasoline demand was met with biofuels and 4.8 percent of the nation's electricity was generated by wind, solar and geothermal last year.
CLEAN ENERGY: Energy that pollutes less than coal and oil, the dominant sources of fuel for electricity and transportation. Natural gas is considered by some, including the Obama administration, to be clean because it emits far fewer pollutants than coal or oil. Nuclear power is also considered clean by some, because nuclear plants emit no greenhouse gas or other pollutants into the air. Others consider only renewable energy truly clean.