Simulation as a methodology is a widely used tool in scientific research, as well as in industrial product development. As simulation has become an established practice in many fields of scientific research, discussions arise about what simulation is. While engineering and natural sciences take a technical position in this discussion, philosophy tries to classify and identify simulation by means of scientific theory and the epistemology of science. This article will attempt to look at these approaches by formulating, from a technical background, questions relevant to philosophy and social sciences in order to understand simulation. In the end, we will find that a coherent theory of simulation is missing, although key building blocks for such a theory do already exist.