Recuperation represents a body's supernatural (or at least extraordinary) ability to rebound from Afflictions, ranging from Diseases to "never-healing wounds". A fellow with Recuperation can even regrow lost limbs. This happens outside of battle.

Recuperation is not Regeneration, a trait that acts quickly enough to prevent the Afflictions from mattering to begin with. It doesn't restore lost Hit Points, and it doesn't stem Profuse Bleeding. Since units who aren't dead (or Diseased) recover all of their Hit Points after the Army Phase battles, though, Recuperation has its own distinct role: keeping your elite combatants functional on the campaign trail.

Recuperation is rare enough to be a selling point; the Pangaeans have it, the Sacred Knights of Early Ermor have it, and the ubiquitous Earth Serpent Pretender Chassis has it. The "white magic" of structural healing is tenuously a Nature art, but it's incredibly rare; if you really need it for someone, your only sure-fire bet is to have it in your Bless, though having it available at the start of the game doesn't come cheap.

Recuperation is a luxury afforded to living beings. It doesn't work for Undead and the Inanimate, even if you were somehow able to apply it to them. It doesn't work for the old, either; every creature must accept an end.

The following is paraphrased from the Dominions 5 wiki, and might not be perfectly accurate to the current version.

A being with Recuperation recuperates after almost everything else in the turn order, including after units age. It can only remove one affliction per turn/month, and it isn't guaranteed to remove any. If Recuperation fails at fixing an affliction (or if the affliction it would fix isn't present), it moves to try and fix another, in a set order of priority.

The priority is as follows, from highest to lowest:

1. Battle Fright (the Morale penalty): 50% chance
2. Feebleminded (the Head affliction that prevents spellcasting and leading units): 25% chance
3. Dementia (the Head affliction that resembles Confusion): 50% chance → 0% if you're still Feebleminded
4. Disease (the Torso affliction that slowly kills you outside of battle): 50% chance
5. Crippled (the Leg affliction that minimizes Map Movement and Combat Speed): 25% chance
6. Blind (the Head affliction that hampers Attack Skill, Defence Skill, and Precision): 25% chance → 0% if your head is missing
7. Lost Eye (the Head affliction that's a lesser form of Blindness): 50% chance → 0% if your head is missing
8. Weakness (the Arm affliction that lowers Strength): 50% chance
9. Mute (the Head affliction that reduces Magic levels and Leadership): 25% chance → 0% if your head is missing
10. Lost Head (the Head affliction that instakills most living units): 20% chance
11. Lost Arm (the Arm affliction that removes an Item/equipment slot): 25% chance
12. Lost Eye (yes, this gets two chances): 50% chance
13. Chest Wound (the Torso affliction that increases Encumbrance): 50% chance
14. Limp (the Leg affliction that's a lesser form of Crippled): 50% chance
15. Never Healing Wound (the Torso affliction that decreases max HP): 10% chance

Note that several of these Affliction types can stack; you can lose more than one eye and more than one arm, for example. Recuperation removes only one instance of these.