A model is a "simplified description of a complex entity or process". It often highlights some feature of the modeled entity or process by blatantly ignoring others. For example scale models of some particular airplane (e.g. XR-71) are faithful in appearance, but can't fly' other models of that same plane can fly but don't look much like an XR-71. Other models are not tangible, e.g. computer models of a nuclear reactor designed to simulate its performance.
According to David Hestenes, one of the founding fathers of modeling instruction,
...
A useful model fits many real situations to a good approximation. Some useful models used by physicists to think about the physical include: motion with constant acceleration, the harmonic oscillator, the two level quantum system, Feynman diagrams and the Schwartzschield metric (which applies the law of General Relatively to find the warping of space-time due to a central sphere of matter). A list of models of mechanics is available.
...
Pedagogical Usefulness
The key pedagogical reason for using models in this course is to provide a framework within which students can organize the many facts and procedures they learn in introductory physics into a small number of useful models, relate these models to the few overall theories that underlie the material, and think about the real world by recognizing situations or simplifications where these models apply. This leads to an understanding of the world, and the ability to simplify and model physical situations that are new. From an expert/novice perspective models organize the many formulae and graphs on the novice's formulae sheet into a much smaller number of "chunks" of related things that are of reflective of nature's organization.
...