Clark Aldrich: A learning simulation is an experience designed to rigorously help users develop competence and conviction. A learning simulation is a combination of modeling elements, entertainment (or game) elements, and instructional (or pedagogical) elements. These can range from pure media (which do not involve any other humans), to experiences that use coaches, teammates, competitors, and communities.
Learning simulations historically have fallen into two categories. There are educational simulations that follow the rigor and fidelity of a flight simulators. And there are serious games, that follow the entertainment model of a SimCity.