In computer graphics, what's the difference between a UVW mapping and a UV mapping?

Question

In working with textures, does "UVW mapping" mean the same thing as "UV mapping"?
If so why are there two terms, and what is the "W"? If not, what's the difference between them?

[Wikipedia currently isn't illuminating on this question: http://en.wikipedia.org/wiki/Talk:UVW_mapping]

Answer 1

U and V are the coordinates for a 2D map. Adding the W component adds a third dimension.

It's tedious to say the least to actually hand generate a 3D texture map, but they are useful if you have a procedural way to generate texture data. E.g. if you wanted your object to look like it's a solid chunk of marble, it may be easiest to "model" the marble "texture" as a 3D procedural texture and then use 3D coordinates to draw data out of the procedural texture.