Shading models.
A shading model is a mathematical formula to compute the surface characteristics and it determines how a surface is shaded. A shader or a material is an implementation of a shading model.
The characteristics of the shading models in your scene have a dramatic impact on the choices you make in lighting.

	Diffuse reflection simulates the light that penetrates a surface and gets reflected by the surface in all directions. Diffuse reflection is the brightest when the normal vector of a surface points toward the light source. Diffuse reflection has nothing to do with the position of your eye (or camera). In order to make a surface “matte,” increase the diffuse reflection and decrease the specular reflection. Lambert shading model simulates diffuse reflection but not specular reflection.
	Specular reflection is the direct reflection of light by a surface. Shiny surfaces reflect almost all incident light and therefore have bright specular highlights or hot spots. The location of a highlight moves as you move your eye (view dependent), while keeping the light source and the surface at the stationary positions. In order to make a surface mirror-like, decrease the diffuse reflection and increase the specular reflection. Phong and Blinn shading models simulates specular reflection, as well as diffuse reflection. Blinn takes into account changes in specularity due to the angle you are viewing the surface at, but not Phong. Phong E which is available in Maya is a simplified version of Phong. The order of rendering performance from fastest to slowest is: Phong E, Phong, and Blinn.
	Ambient reflection is a gross approximation of multiple reflections from indirect light sources (e.g., the surfaces of walls and tables in a room that reflect off the lights from light sources). Ambient reflection produces a constant illumination on all surface, regardless of their orientation. If you look at the faces of a cube to which only ambient reflection is applied, all the faces are illuminated by the same amount of light. Ambient reflection itself produces very little realism in images.
	The light reflected from a typical surface in the real world is a combination of the above three reflections.

Read Birn's 9.1.1-9.1.2 (Pages 193-196). For information on attributes of the surface materials available in Maya, see Using Maya -> Rendering -> Surface Materials. And also Using Maya -> Rendering -> Material Attributes -> Common material attributes.