Version: 2019.2
public Terrain.MaterialType materialType ;

Description

The type of the material used to render the terrain. Could be one of the built-in types or custom. See MaterialType.

If you want to use a custom material, set this to Terrain.MaterialType.Custom, then assign a material to Terrain.materialTemplate. Terrain.MaterialType.Custom with Terrain.materialTemplate == null is identical to Terrain.MaterialType.BuiltInLegacyDiffuse.