HDR is short for High Dynamic Range. It is a software technique of taking either one image or a series of images, combining them, and adjusting the contrast ratios to do things that are virtually impossible with a single aperture and shutter speed. Although not for every photograph, I think you will agree that the results are stunning.
There is an awesome tutorial at stuckincustoms.com on how to generate HDR images from the picture you take with your digital camera. Although the results are far more impressive with multiple RAW source images (you’ll need an auto-bracketing capability and a tripod), the technique can be applied to single JPG images shot with a point-and-shoot digital camera. I have included some sample images (courtesy stuckincustoms.com), but I would encourage you to go to that site or to the author’s HDR gallery on Flickr to see some truly amazing images.
Images courtesy stuckincustoms.com