Model (mathematical model) : A physical or mathematical representation of a natural system (reality) intended to mimic the behavior of the real system, allowing description of data and predictions about the system
U.S. Environmental Protection Agency, Radiation Glossary, Office of Radiation and Indoor Air Radiation Protection Division, Washington, DC, USA 2013. http://www.epa.gov/radiation/glossary/index.html#a , (Dzstr/ Rad Emr - Amer) {823}