Material
Materials are a concept in 3D rendering that describes how to render a particular surface. Each render chunk is comprised of a single material, a vertex buffer, and an index buffer.
Each material is defined with a material type, one or more texture files (eg. a Diffuse map, Normal map, etc.) and some number of other parameters (strength, scale, color, etc.)
Materials do not exist as individually editable files, but typically reside within other files such as trainzmesh files. Each material is assigned a unique identifier (typically composed from the parent asset's KUID and a material name assigned in a modeling package such as Autodesk 3ds Max. This means that it is possible for meshes within the same parent asset to share materials, but it is not possible for meshes in separate assets to (accidentally, or deliberately) share materials. Where deliberate material sharing is desired, content creators may make use of a mesh library which is a non-placeable asset containing a number of meshes and textures acting as a common storage for the actual placeable assets.