Meteorol. an optical phenomenon, usually in polar regions, in which the snow-covered ground blends into a uniformly white sky, greatly reducing the visibility of shadows, clouds, the horizon, etc. and one's sense of direction or distance
See whiteout in American Heritage Dictionary 4
A polar weather condition caused by a heavy cloud cover over the snow, in which the light coming from above is approximately equal to the light reflected from below, and which is characterized by absence of shadow, invisibility of the horizon, and discernibility of only very dark objects.
A fluid, usually white, that dries quickly and is applied to printed matter to cover mistakes.