HDR
High dynamic range: highlights brighter than a normal screen white, with detail kept in the dark.
See it in WebGL playground. Raise Bloom: its glow imitates light brighter than the screen can show.
In plain words
In a normal picture, white is the brightest anything can be. Real sunlight, flames and reflections are far brighter than that. HDR pictures store brightness above normal white, and HDR screens can light those parts more strongly. Detail in dark shadows is kept too. On a normal screen the extra range has to be squeezed down to fit.