Cogito, ergo sum
The UV2Texture allows a material to be superimposed on a static mesh, overriding (or overlaying on) the default material of the static mesh. This is set with the UV2Texture and UV2Mode properties inthe Display properties group.
The main use for this property appears to be to add a custom lightmap on a static mesh. Such a lightmap must be mapped to the object underlying the static mesh using the second UV channel (in 3D Studio Max terminology, I believe) or the UV map named 'UV2' (in Lightwave; it is essential that this exact name be used for the UV map). For an example of this, see the static mesh (in MyLevel) corresponding to the central chamber in DM-Antalus.
Fat Marrow:This would ideally also explain about UV2Mode, if I knew how that worked, and refer to other (non-Lightwave) UV topics.
Tarquin: good start though. I've interlinked a bit more.