What is "deep sleep"

n. 1 (&lit deep sleep English) 2 (context rare fiction English) Artificially induced hibernation in humans for the purpose of long distance space travel.

Deep Sleep is a 2012 point-and-click adventure game by Scriptwelder. It is a free browser game in which players attempt to navigate a dream world inhabited by shadow people. It was designed for and won first place in the 2012 Jay Is Games Casual Gameplay Design Competition.