END or Equivalent Narcotic Depth is used to express the relative narcotic effect of nitrogen at given depths. Also called rapture of the deep, it impairs divers when they get exposed to a certain pressure. It is different for every diver at different times. The END compares a mixed gas other than air such as nitrox or trimix to what the narcotic effect would if the dive was conducted on air.
Narcosis also called nitrogen narcosis or inert gas narcosis is the name of the impairment that affect divers when the nitrogen in what we breath becomes narcotic under pressure. It has been given the name of rapture from the deep by Jacques Cousteau when divers started pushing the depth limits of diving beyond the 30 meters mark.