Parallax map or Photonic Mapping, Offset Mapping, Virtual Displacement Mapping (call it as you want :D ) is a new kind of " bump mapping " it enhances the sensation of depth.
For more details on parallax map visit -> Wiki paralax mapping


let's compare :
Before : Original after :Parallax mapping

You can try a demo concerning the technique of prallax mapping here 
The demo is developped with Virtools Dev 3.5. To play the Demo Download the Virtools player

Enjoy :)