I've read UVW somewhere as well. We have to find out more.
For UVW mapping Wikipedia says no more than: "the third dimension allows texture maps to wrap in complex ways onto irregular surfaces"
A Google search shows UVQ is mostly related with SketchUp, and that the names of these coordinates are not very standardized (just letters in the alphabet before x,y,z), for example there are also Q,R,S,T.
There's an interesting explanation on gamedev.stackexchange, that the W allows to optionally apply a transformation matrix before rendering a texture to screen (for example for animating textures without expensive moving of the texture on every entity).