Simulation is the process of mimicking the behaviour of a real physical process or system using a representative model.
Simulation is the process of mimicking the behaviour of a real physical process or system using a representative model. It assumes that in a first step, a model is built that captures the key characteristics of the real world system. As real world systems tend to be very complex, the modeler has to make assumptions and simplifications. Therefore, it is important that the modeler verifies and validates her model to assure that indeed the right "physics" of the real world is represented in the model.
In a next step, a computer program or algorithm is used to evaluate the equations that result from the modeling step. Because of the possible complexity of the model, this can require again approximations like model simplifications and/or discretisation of continuum equations.
Sometimes the simulation can be run using Monte Carlo simulation: a process where by using (pseudo-)random variables, the model can be sampled and an average behaviour can be predicted.