Clinical models are representations of physiological and pathological phenomena that are used for predicting patient evolution.
A simple example is a diagnostic class. For example, we say 'this patient has cholera'. By this statement we refer to a mental representation of a particular bowel infection, with a particular organism (vibrio cholerae) and we use it to predict the possible evolution of the patient (massive diarrhea followed by spontaneous healing, or by death if dehydration is not kept under control).
A particular patient may not progress as predicted by the mental representation (clinical model) for a variety of unknown reasons, but fact is that the prediction is always made based on some representation. So, the term 'clinical model' does not refer to the patient but what the doctor thinks, correctly or not, that is happening to a particular patient.
Much of the progress of medical practice actually consists in improving the predictive accuracy of such models. While clinical models are, obviously, as old as medicine, only recently have they been named as such and thus became objects of study.
This site is dedicated to gathering information about quantitative clinical models that are starting to be used in patient prediction, whether thay are called like that or not.