Death Saving Throw
When a character is reduced to below zero Hit Points, the player may elect to make a final saving throw against death, and if successful the character will return after the combat or other damaging incident is concluded with a single hit point, gravely injured.
In this state a character cannot act in combat or engage in dungeoneering tasks unless healed. Additionally should a character that is gravely injured take any damage, it is a killing blow, without further recourse to the death save.
Death saves are static, but increase (making survival less likely) each time the character makes one. All characters begin with a Death Save of 10, but this increases by one point each time they roll against it.
Credit: Dungeon of Signs house rules document.