Layer Weight Node
The Layer Weight node outputs a weight typically used for layering shaders with the Mix Shader node.
Bias the output towards all 0 or all 1. Useful for uneven mixing of shaders.
Input meant for plugging in bump or normal maps which will affect the output.
Dielectric Fresnel weight, useful for example for layering diffuse and glossy shaders to create a plastic material. This is like the Fresnel node, except that the input of this node is in the often more convenient 0.0 to 1.0 range.
Weight that blends from the first to the second shader as the surface goes from facing the viewer to viewing it at a grazing angle.