Although newer version of Maya have incorporated Solid Angle’s Arnold renderer. NVIDIA’s (formerly mental images) mental ray is still used in production quality rendering.
People coming from Maya’s basic shader e.g. Phong, Blinn, Lambert don’t get daunted watching the mental ray shaders. So today I’ll explain what they actually mean.
**mi - **mi is short for mental images, the facility in which mental ray was developed. You now know what is that mi in all the shaders.
mib - b is for base. Are they base materials?
mia - a is for architecture. Anything not containing any living organism maybe. More information can be found in mental ray documentation.
misss - sss is for subsurface scattering. Wikipedia has a good explanation of it.
mila - l in mila stands for layering. So shaders are also layered to achieve a good result. More information can be found at elemental ray blog.
Now you have basic knowledge of shaders. Now you can anticipate about car_paint and metallic_paint shader groups (libraries).