There is dispute about what exactly a “mental model” is and the concepts related to it are often aren't clarified well. One feature of them that is generally accepted is that “the structure of mental models ‘mirrors’ the perceived structure of the external system being modelled.” (Doyle & Ford, 1998, p. 17) So, as a starting definition we can say that mental models, in general, are representations in the mind of real or imaginary situations. A full definition won’t be attempted because there is too much contention about what features mental models do and do not have. The features that are accepted will be described in detail which will hopefully lead you to gain a intuitive understanding of what mental models are probably like.