The aura of life spell description (PHB, p. 216) states:
Life-preserving energy radiates from you in an aura with a 30-foot
radius. Until the spell ends, the aura moves with you, centered on
you. Each nonhostile creature in the aura (including you) has
resistance to necrotic damage, and its hit point maximum can’t be
reduced. In addition, a nonhostile, living creature regains 1 hit
point when it starts its turn in the aura with 0 hit points.
Does "living" here mean:
has 1 HP or more?
or
not undead or death state?
Best Answer
It heals undeads
In 5e, "Undead" is just another type of creature - like Dragon or Giant - and is not dead. These are described in the beginning of the Monster Manual (specifically, pages 6 and 7).
Healing spells that don't affect undeads explicitly say so, e.g. Cure Wounds
Additionally, some spells, like Raise Dead, say
This means an Undead creature was alive to begin with (dying does not change the type of a creature, i.e. if you cast revivify on a zombie, you revive the zombie, not the original creature).
As a note, "Dead" is not a condition in 5e, mechanically speaking. Death actually changes the creature from Creature to Object (corpse is an object).