I'm not sure which of the first 3 may correspond to what, but this is what they're using, as it's the same kind of thing we use at my job:
1) Color map - The visible texture of what something looks like.
2) Specular map - Greyscale image. The whiter, the more specular. The darker, the less.
3) Bump map or Hieght map - Greyscale image. The whiter, the higher.
4) Normal map - The purple hued image. This is a light information map and tells each pixel how to react to light sources, so you can essentially have shadows from a detail that isn't actually there.... just an image.
Other maps that are also used:
- Opacity map aka Transparancy map - Greyscale image. White areas are opaque, black transparant.
- Incandescense(sp) map - Greyscale image. White areas are self-illuminated and will "glow" in the dark.
- Reflectivity map - Greyscale image. White areas are reflective.
- Offset map - Greyscale image. Similar to hieght map.