Model

In science, a model is an aid to understanding that represents an unseen or complex phenomenon.

Models can be empirically found, or derived from fundamental laws. A good model has a well-defined domain of validity, in which it leads to unambiguous, self consistent results. Ideally it is easy to evaluate. To adaption of a model to a specific problem instance is done by model parameters, which can be defined/measured independently or left as free parameters to fit the model to a realistic situation. A large number of free parameters makes it difficult to assess the validity of the model without independent knowledge.