A model is a representation of a real world system. In most cases, they are a simplification of this real world. Models are used extensively within all fields to better understand any system. Ranging from cosmic events to the model of an atom. Models also help us predict the behaviour and manipulate outcomes of systems. There are 2 components to the use of models, one is the academic aspect and the other is the application aspect.

Models can be mathematical. If the behaviour of a system can be represented by a set of parameters and the relation between these parameters can be deduced via experiments, natural observation, logical reasoning etc.

Models can be more abstract than a set of equations. Models can be in the form of data in tables, like financial models in a spreadsheet. A flow chart can be used to represent a process and interaction between stages in a process. Models can be a block diagram that breaks down a system into its constituents and shows the relation and interaction between them. These kind of models are widely used within the realms of systems engineering. Thought processes and intuitive perception can be expressed using mental models. Mental models are just explanations of thought processes.

In a nutshell, models can take a form of numbers, equations, diagrams or text.