n. 1a. a fragment of a mathematical or formal theory that reflects some aspect of a particular physical, social, technological or natural phenomenon or process and enables predictions to be made about its behaviour. For example, it is possible to construct a computer mode of the national economy in order to test the probable results of certain changes in government policy. See input-output model.
b. vb. to abstract such a mathematical description of some process. 2. formally, a theory in which a given sentence or set of sentences is true. For example, Peano's axioms have a model in arithmetic (their intended interpretation) but they also have non-standard models that are not isomorphic to arithmetic. 3. (Logic) an interpretation of a formal calculus under which the theorems derivable in that system are assigned the value true, that is are mapped onto truths.