Texture

An image or graphic which can be applied to a surface.

Level textures are skinframes

In Darkplaces engine engine each level and model texture is represented by skinframe.

Skinframe is a set of images containing base texture and additional textures prefixed with special word and used to store additional information:

_norm - normalmap texture for per pixel lighting (alpha stores heightmap for parallax mapping)
_gloss - specular texture for per pixel lighting, can be in color (alpha stores gloss exponent)
_glow - fullbrights or other glowing overlay stuff (this is done using additive blend, not alpha)
_pants - pants overlay for colormapping on models, should be shades of grey (it is tinted by pants color) and black wherever the base texture is not black, as this is an additive blend
_shirt - same idea as pants, but for shirt color
_reflect - mask for cubemap reflection texture

Sample:

textures/inn/table.tga // base texture
textures/inn/table_norm.tga // normalmap
textures/inn/table_gloss.tga // specular texture

Important: Skinframe is not a skin.