(1) A physical, mathematical, or otherwise logical representation of a system, entity, phenomenon, or process. (DoD 1998)
(2) A representation of one or more concepts that may be realized in the physical world. (Friedenthal, Moore, Steiner 2009)
(3) A simplified representation of a system at some particular point in time or space intended to promote understanding of the real system. (Bellinger 2004)
(4) An abstraction of a system, aimed at understanding, communicating, explaining, or designing aspects of interest of that system (Dori 2002)
(5) A selective representation of some system whose form and content are chosen based on a specific set of concerns. The model is related to the system by an explicit or implicit mapping. (Object Management Group 2010)
(1) DoD. 1998. "'DoD Modeling and Simulation (M&S) Glossary" in DoD Manual 5000.59-M. Arlington, VA, USA: US Department of Defense. January. P2.13.22. Available at http://www.dtic.mil/whs/directives/corres/pdf/500059m.pdf
(2) Friedenthal, S., A. Moore, R. Steiner, and M. Kaufman. 2012. A Practical Guide to SysML: The Systems Modeling Language, 2nd Edition. Needham, MA, USA: OMG Press.
(3) Bellinger, G. 2004. Modeling & Simulation: An Introduction. Accessed on 11 September 2012. Available at http://www.systems-thinking.org/modsim/modsim.htm.
(4) Dori, D. 2002. Object-Process Methodology: A Holistic System Paradigm. New York, NY, USA: Springer.
(5) Object Management Group. 2010. MDA Foundation Model. OMG document number ORMSC/2010-09-06.
See also model management, model validation, model-based systems engineering (mbse) , modeling language and modeling tool.