Models are representation of reality in a form that helps in understanding and visualising the nature of the reality represented by the model, and in analysing the relationships between different factors impacting the reality. The models can represent the reality using different representation techniques such as verbal descriptions, mathematical formula, graphs, diagrams, pictures, and two or three dimensional physical models. The models always represent some aspect of the reality and not the whole reality. But a good model concentrates on representing in convenient form the aspect of reality that are most relevant for decision making in specific situation. Models also permit examination of the likely behaviour of the reality under different alternative situations, without all the expenditure of time money and risk that will be involved manipulation of the actual reality. For example the aerodynamics of a new aeroplane under development can be studied examining behaviour of a small model of the aeroplane in a wind tunnel.
In this way models help in the decision making process by aiding understanding of the reality by simplifying it, and permitting experimentation with reality in a quick, economic and risk free way.