High Dynamic Range is a technique whereby you shoot a series of images of the same scene, taking care to have your camera abolutely still (tripod with cable release). Using an Auto Bracketing feature of your camera, if it has one, each image in a sequence has different exposures from very overexposed to very underexposed and a number of images in-between. The sequence images are then dropped into special HDR software where they are stacked, aligned and then "tone mapped". In so doing, you get an exceedingly wide tonal range to your one resulting image.