3D Light
Diffuse Light

Ambient Light
Light from everywhere.
Diffuse + Ambient (lights the previously black as well as everything else).

Specular Light / Specular Highlight
The specular highlight makes the object seem to reflect light.
Diffuse + Ambient + Specular:

Images from http://www.directxtutorial.com/Lesson.aspx?lessonid=9-4-3