Energy moving in the form of particles or waves. Familiar radiations are heat, light, radio waves, and microwaves. Ionizing radiation is a very high-energy form of electromagnetic radiation
Centers for Disease Control and Prevention, Emergency Preparedness and Response, Radiation Emergencies, Radiation Dictionary, U.S. Department of Health and Human Services, Atlanta, GA, USA 2011. http://emergency.cdc.gov/radiation/glossary.asp, (Dzstr/ Rad Emr - Amer) {820}