A material's components describe its visual and optical properties. The components include its color components, highlight controls, self-illumination, and opacity.
A surface of a "single" color usually reflects many colors. Materials use multiple colors to simulate this:
Diffuse color is the color of the object in direct, "good" lighting.
Ambient color is the color of the object in shadow.
Specular color is the color of shiny highlights.
Self-illumination simulates an object lit from within.
Opacity is the opposite of transparency. As you reduce the Opacity value, the object becomes more transparent.
Bump is a component that uses a map to simulate bumpiness.
You can assign maps to most components, including color components such as Diffuse, and value components such as Opacity. Maps can increase the complexity and realism of the material's appearance.