Hi Mark,
An HDR image is a series of digital images of a subject, with some frames exposed for the highlights and some for the shadows, then combined back into one image using Photoshop or other software. The resultant image is supposed to show the full range of shadows and highlights - hence the name, High Dynamic Range.
When done well, some HDR photography can be stunning. However, I find that most of it looks unnatural - halos, strange colours, weird looking scenes - the example you've posted I would class as "disastrous"!
Have a look at http://www.stuckincustoms.com/ for some examples of some of the better HDR photography.
Just out of curiosity - why would that example be "disastrous"? Anyone?
Quite simply, HDR mean high dynamic range. Many cameras today can do internally what the guys above are doing with post processing. The HDR setting in the camera simply exposes for the highlights then boosts the shadows to provide low-light detail before saving the picture. If you're used to shooting only jpegs, it's a useful technique to avoid over-contrasty pictures, but it can introduce excessive noise if overdone. If you shoot raw, then mostly you can get a better result by using the raw processor in your PC's photo program.
...But the problem I find with HDR is that it rarely looks natural...
