Usage of texture:
wall - vertical wall textures, natural or man-made
floor - floor textures, either natural(ground) or man-made
ceiling - anything that was made to be used as a ceiling
roof - rooftop textures for buildings
door - any door texture, including gates
window - any window texture, including the window frames
sky - sky's....DUHHHHHH ;)p
signs - anything that has verbage on it, posters, signs
road - road, paths and trails
pipe - pipe textures, valves for pipes, also includes wires
flat - anything that produces an even, non-bordered pattern in all directions
special - made for brush objects ONLY (i.e. crates, boxcars)
indoor - pictures, misc household items
trim - all trim, including ibeams, endcaps, etc...
masked - any texture that has alpha'd areas (like handrails, grates, etc...)
damaged - anything that's been damaged (has blast marks, burns, etc...)
utility - textures like nodraw, caulk, trigger, etc.... ONLY!
terrain - only put this on textures made specifically for the terrain system
panel - paneled type textures (like the library ones)
light - light emmiting textures

Material types:
metal - all types of metal
rusted - rusted, weathered metal
corrugated - corrugated materials
gravel - gravel textures
sand - sand textures
rock - naturally occuring rock formations (walls, floors, etc...)
stone - man-altered rocks like stone walls, cobblestone streets, also tile
brick - brick textures
concrete - concrete textures
wood - wood textured
plaster - plaster textures
carpet - carpet and cloth type textures
liquid - all liquids, including oceans, rivers, puddles, etc....
river - river textures, or other flowing water types
ocean - ocean textures
glass - glass textures
tudor - used in french/german towns with plaster sandwiched between wooden beams
natural - non man-made materials
dirt - all dirt textures, including transitional textures with dirt
grass - all grass texture, including transitional textures with grass
tree - textures relating to trees
bush - textures relating to bushes
folliage - vines, forest canopy, underbrush
snow - if the texture has any snow or ice on it
mud - if the texture is, or has mud on it

Level Reference: - meaning the texture was made for a particular mission
m1 - North Africa
m2 - D-Day, Normandy, Nebelwerfer
m3 - OSS mission in France, blow train rails, manor house
m4 - Brest France, Artillery missions, sniper hunt
m5 - snow forrest, snow town/train station, schmertzen
m6 - Hunt artillery, Ramagen
m7 - U-Boats in Norway
intro - opening cinematic
ending - ending cinematic