Descriptive Model (glossary)
(1) A model that describes things as they are. (Turban, et al 2010)
(2) That depicts or describes how things actually work, and answers the question, "What is this?" (BusinessDictionary 2012)
Sources
(1) Turban, E., R. Sharda, and D. Delen. 2010. Decision Support and Business Intelligence Systems, 9th ed. Upper Saddle River, NJ, USA: Prentice-Hall.
(2) BusinessDictionary.com. 2012. s.v. "Descriptive Model." http://www.businessdictionary.com/definition/descriptive-model.html (accessed: September 12, 2012).
Discussion
Typical descriptive models may include those that describe the functional or physical architecture of a system, or the three dimensional geometric representation of a system.