http://en.wikipedia.org/wiki/High-dynamic-range_imaging

High-dynamic-range imaging (HDRI or HDR) is a set of techniques used in imaging and photography to reproduce a greater dynamic range of luminosity than possible using standard digital imaging or photographic techniques.
HDR images can represent a greater range of luminance levels found in real-world scenes, from direct sunlight to faint nebula. It is often achieved by capturing and then combining different exposures of the same subject matter.[1][2][3][4] Non-HDR cameras take photographs with a limited exposure range, resulting in the loss of detail in bright or dark areas.

Trey’s Complete HDR Tutorial