The Velvet BSDF is used to add reflection to materials such as cloth. It is meant to be used together with other shaders (such as a Diffuse Shader) and is not particularly useful on its own.
Color of the surface, or physically speaking, the probability that light is reflected for each wavelength.
Variance of the normal distribution, controlling the sharpness of the peak. It can be thought of as a kind of roughness.
Normal used for shading; if nothing is connected the default shading normal is used.
Standard shader output.