All and none
From the beginning, hit points were an abstract resource system derived from managing unit cohesion coupled to a role playing framework.
Hit points are and always have been a fantasy resource that role players could use without the distraction of actual wounds, and the consequences there-of.
Hit points have always been weakly coupled to physical damage, but only weakly. They can be mapped to any of actual damage, morale, exhaustion, mental fatigue, ablated luck, or none of those, under the control of the players and the game master. The abstraction, I believe, was never meant to necessarily map to any of the preceeding, but could be, if that is what you wanted.
Put another way, hit points, to stay useful, have to stay only very roughtly mapped to any actual damage system.
What hit points become, as used, is a means of narrative control: A player can operate toe-to-toe to a physical adversary for so long, but for only so long, but they can keep going when they share the narration with the other folks in the party.
TomB