Advanced Surface Definitions
Surfaces in ArmA are no longer just simple color textures but more advanced structures composed from multiple textures and other additional information that tells the engine how to represent the surface. See ArmA:RVMAT for info about material definition files. See ArmA: Texture Naming Rules for a list of the various texture types used.
A little bit of theory: http://en.wikipedia.org/wiki/Bidirectional_reflectance_function