"HDR" is an acronym for high dynamic range. In photography, it means the ability to create photographs with a much greater range of color saturation than traditional photographs.
High dynamic range images are achieved by taking multiple photographic exposures and combining the best of each into a single photograph. When taking pictures, photographers often need to gird their exposure to specific parts of the image they're shooting, forsaking other areas. With HDR photography, they vary the exposure in several different otherwise identical shots, and all the images are combined to yield the final photograph.
We bring this up because a number of today's cameras include an auto HDR capability. Set the camera to auto HDR, and the camera automatically takes a number of pictures of the same view, then creates an HDR image. One of our first experimental attempts to use auto HDR is a cloud shot occasionally on our Jeff Berger Facebook page. (It's a start...)
An explanation of HDR is here: http://en.wikipedia.org/wiki/High_dynamic_range_imaging
You'll find many sample HDR images here: http://bit.ly/MT7CyW