Textures
General
X-Plane uses a lot of textures for a lot of differing things. Over the years, many of the textures have come to be known by quite specific proper names. While these names are unofficial, over time they have infiltrated the X-Plane developer lexicon enough to become standardized. With regards to aircraft and scenery development, some of these proper names are:
Textures for OBJs are assigned to the OBJ via the Scene Tab > OBJ Meta-Data > Textures Sub-Panel
ALB - Albedo Textures
NML - Normal Texture
See Article HERE on Normal Maps