A computer model is an abstract mathematic representations of a real-world event, system, behavior, or natural phenomenon. A computer model is designed to behave just like the real-life system. The more accurate the model, the closer it matches real-life. 
A computer model is a translation of objects or phenomena from the real world into mathematical equations.
Why use a model
Thanks to https://www.igcseict.info for the content below. A model might be used:
- To test a system without having to create the system for real (Building real-life systems can be expensive, and take a long time)
- To predict what might happen to a system in the future (An accurate model allows us to go forward in virtual time to see what the system will be doing in the future)
- To train people to use a system without putting them at risk (Learning to fly an airplane is very difficult and mistake will be made. In a real plane mistakes could be fatal!)
- To investigate a system in great detail (A model of a system can be zoomed in/out or rotated. Time can be stopped, rewound, etc.)
Constructing a model
Model Construction Principle: Problems must be designed to allow for the creation of a model dealing with:
- Relationships and operations between these elements
- Patterns and rules governing these relationships
What is a useful model?
Two different types of models
A model or simulation where no randomness is involved.
stochastic A model or simulation that uses random numbers so that the system states and the output results are not exactly predictable from run to run.
Do I have a model?
- I have identified important features / factors of whatever event(s) I hope to represent.
- I identified rules that control those features and their relationships.
- I have mathematically expressed those rules
- I have adjusted for how likely each factor is.
- Define the term computer modelling.