acid rain - the precipitation of dilute solutions of strong mineral acids, formed by the mixing in the atmosphere of various industrial pollutants -- primarily sulfur dioxide and nitrogen oxides -- with naturally occurring oxygen and water vapor.

act - in the legislative sense, a bill or measure passed by both houses of Congress; a law.

adjournment - the end of a legislative day or session.

aerosol - a suspension of small liquid or solid particles in gas.

air pollution - toxic or radioactive gases or particulate matter introduced into the atmosphere, usually as a result of human activity.

alternative energy - energy that is not popularly used and is usually environmentally sound, such as solar or wind energy (as opposed to fossil fuels).

alternative fibers - fibers produced from non-wood sources for use in paper making.

alternative fuels - transportation fuels other than gasoline or diesel. Includes natural gas, methanol, and electricity.

alternative transportation - modes of travel other than private cars, such as walking, bicycling, rollerblading, carpooling and transit.

amendment - a change or addition to an existing law or rule.

ancient forest - a forest that is typically older than 200 years with large trees, dense canopies and an abundance of diverse wildlife.

apportionment - the process through which legislative seats are allocated to different regions.

appropriation - the setting aside of funds for a designated purpose (e.g., there is an appropriation of $7 billion to build 5 new submarines).

aquaculture - the controlled rearing of fish or shellfish by people or corporations who own the harvestable product, often involving the capture of the eggs or young of a species from wild sources, followed by rearing more intensively than possible in nature.

aquifer - underground source of water.

arms control - coordinated action based on agreements to limit, regulate, or reduce weapon systems by the parties involved.

ash - incombustible residue left over after incineration or other thermal processes.

asthma - a condition marked by labored breathing, constriction of the chest, coughing and gasping usually brought on by allergies.

atmosphere - the 500 km thick layer of air surrounding the earth which supports the existence of all flora and fauna.

atomic energy - energy released in nuclear reactions. When a neutron splits an atom's nucleus into smaller pieces it is called fission. When two nuclei are joined together under millions of degrees of heat it is called fusion.