Microgeometry
Microgeometry is the minute geometric irregularities found on a surface. It shares similarities with nanogeometry, albeit on a larger scale—larger than the wavelength of light but still smaller than a pixel.
Microgeometry tilt the surface in various directions. We can view it as changing of local normal.
Typically, we model microgeometry as a statistical aggregate, providing the foundation for the microfacet theory employed in physically-based rendering.