“High-dynamic-range imaging (HDRI or HDR) is a technique used in imaging and photography to reproduce a greater dynamic range of luminosity than is possible with standard digital imaging or photographic techniques. The aim is to present the human eye with a similar range of luminance as that which, through the visual system, is familiar in everyday life. The human eye, through adaptation of the iris (and other methods) adjusts constantly to the broad dynamic changes ubiquitous in our environment.”
In other words, make some really stunning and dramatic photos that POP! Using HDR techniques might seem a little complicated at first, but once you get the hang of it you will find it an easy way to create some amazing photos.
The tutorial below is another one using GIMP. You can apply the same techniques to Adobe Photoshop if that is your editor of choice.