radioactive - of or characterized by radioactivity.

radioactive waste - the byproduct of nuclear reactions that gives off (usually harmful) radiation.

radioactivity - the spontaneous emission of matter or energy from the nucleus of an unstable atom (the emitted matter or energy is usually in the form of alpha or beta particles, gamma rays, or neutrons).

radon - a cancer-causing radioactive gas found in many communities' ground water.

rainforest - a large, dense forest in a hot, humid region (tropical or subtropical). Rainforests have an abundance of diverse plant and animal life, much of which is still uncatalogued by the scientific community.

ranking member - the lead member of a Congressional committee from the minority party, usually chosen on the basis of seniority.

recess - ending a legislative session with a set time to reconvene.

recycling - system of collecting, sorting, and reprocessing old material into usable raw materials.

reduce - act of purchasing or consuming less to begin with, so as not to have to reuse or recycle later.

refrigerants - cooling substances, many of which contain CFCs and are harmful to the earth's ozone layer.

renewable energy - energy resources such as windpower or solar energy that can keep producing indefinitely without being depleted.

reservoir - an artificial lake created and used for the storage of water.

resolution - a formal statement from Congress.

reuse - cleaning and/or refurbishing an old product to be used again.

rider - usually unrelated provisions tacked onto an existing Congressional bill. Since bills must pass or fail in their entirety, riders containing otherwise unpopular language are often added to popular bills.

riparian - located alongside a watercourse, typically a river.

risk assessment - methods used to quantify risks to human health and the environment.

run-off - precipitation that the ground does not absorb and that ultimately reaches rivers, lakes or oceans.