HDR stands for High Dynamic Range. The essence of HDR is to capture the higher range of contrast us humans view with our eyes and that film and digital receptors cannot capture in a single shot. When we look at a scene we can see more detail in highlights and in shadows than what cameras can record. Hence, the HDR technique.
Fairly new to the photographic world, we can now capture a sequence of exposures and blend them together in an attempt to fill the information gaps mentioned above. Photographers now also have the ability to control the effect of these blends and create mild, almost unnoticable HDRs or extreme and surreal looking HDRs like these ones I did for Avondale. It is great fun and takes the pain out of cloudy and rainy days.
Tips when doing HDRs: Mount your camera to a tripod for stability. Don't waist time between frames. Don't be sidetracked by the tecnique and forget about composition - still make sure you are taking a beautiful photo and then have fun with the process.