A narrow definition of computer graphics would state that it refers to taking a model of the objects in a scene (a geometric description of the things in the scene and a description of how they reflect light) and a model of the light emitted into the scene (a mathematical description of the sources of light energy, the directions of radiation, the distribution of light wavelengths, etc.), and then producing a representation of a particular view of the scene (the light arriving at some imaginary eye or camera in the scene).
In the field of computer graphics, the word “model” can refer to a geometric model or a mathematical model. A geometric model is a model of something we plan to have appear in a picture: We make a model of a car, or a house, or an armadillo. The geometric model is enhanced with various other attributes that describe the color or texture or reflectance of the materials involved in the model. Starting from nothing and creating such a model is called modeling, and the geometric-plus-other-information description that is the result is called a model.