Heightmap is texture containing individual heights used to store terrain data.
Heightmaps textures are used to store geometric detail like terrain, object surface etc. It is used to simplify manipulation of such geometry and even speed up its rendering (if mesh generation moved into shaders).
In case the heightmap is stored in common raster image formats then for proper geometry restoration we need also additional info like: scale,position and orientation for such textures which are not stored in them. So those are usually stored in some separate config file, encoded into filename, or hardcoded into application that uses them.
