It looks like you're new here. If you want to get involved, click one of these buttons!
Props to Kiamde for showing me this....
What is HDRI? In computer graphics and cinematography, high dynamic range imaging (HDRI for short) is a set of techniques that allow a far greater dynamic range of exposures than normal digital imaging techniques. The intention is to accurately represent the wide range of intensity levels found in real scenes, ranging from direct sunlight to the deepest shadows.
This provides the opportunity to shoot a scene and have total control of the final imaging from the beginning to the end of the photography project. A concrete example would be that it provides the possibility to re-expose. One can capture as wide a range of information as possible on location and choose what is wanted later. (JGWill, 2004) - Wikipedia
Here are some pictures of HDRI in effect with Half-Life 2 Models, here
G4TV has an article on how to do all of this, here.