Sim is short for simulation. It is a collective term for a computer software that attempts to accurately simulate an event, situation or phenomenon. It allows the user to observe an activity through simulation without executing that operation.
This type of software is generally used to create a model so that the final product will be as close to the design without costly modification. Real-time response simulation software is frequently used in gaming but also has vital industrial relevance. Costly operations like airplane pilots, chemical and nuclear power plant operators, simulation software gives extremely useful training exercises and experience without