A physical model is a framework of ideas and concepts from which we interpret our observations and experimental results.
In its highest form, a physical model is expressed as a set of natural laws, e.g. Newton's laws of motion or Darwin's law of evolution. Often new discoveries produce a paradox for a current model, such as the photoelectric effect in the early 1900's. New aspects of nature can lead to a new model, or corrections to the old model. For example, special relativity was a modification to Newton's laws of motion to incorporate the effects seen when moving at high velocities and the result of a barrier to velocity of the speed of light.
Excerpt from the Encyclopedia Britannica without permission.