A vast area which includes generating results from computer models.
Simulation is the imitation of the operation of a real-world process or system over time. The act of simulating something first requires that a model be developed; this model represents the key characteristics or behaviors/functions of the selected physical or abstract system or process. The model represents the system itself, whereas the simulation represents the operation of the system over time [wikipedia] .
For understanding when to use simulation , refer to the following question :