Graphical, mathematical (symbolic), physical, or verbal representation or simplified version of a concept, phenomenon, relationship, structure, system, or an aspect of the real world.
A representation of a physical phenomenon built on data (measured and/or theoretical). There are three types of model: Empirical: A model that is based on observations. Physics-based: A model that is
based on first principles. It relies on mathematical descriptions of specific physical phenomena. Semi-empirical: A model that is partially based on observations and partially on first principles.