The Specular parameter is another parameter that will be found with many material types.
Specular reflections are reflections that are bounced off a material surface without scattering. Materials appear reflective or shiny when a surface is polished and has few to no imperfections. When the specular color is set to black, a material will have no specular reflections and will not appear reflective or shiny.
Specular color set to white will give 100% reflectivity for that material. Metals do not have diffuse color so any color will be derived entirely from the specular color. The specular color of plastics should be set to a grayscale value.
The specular parameter will control the color and intensity of the specular light reflections on a material.