There are multiple types of cyborgs in the BTR universe:
Axioms are the most common. They are someone who is mostly human but has robotic parts added to them. They're what you normally think of when you hear "cyborg".
Rapunzels are neurodonors or high-percentage axioms whose brain implant malfunctioned, causing them to become a monster.
Neurodonors are only cyborgs by the barest stretch of the imagination. They are humans who have sold/"donated" their bodies, except for their central nervous system. Their CNS is then implanted into a robotic body, usually of a wolf or horse or other four-legged animal. Their human body is chopped up for parts and sold to finance their robotic one. Technically cyborgs because their brain is human.
Adam/Eve Unit or "users" are humans with computers and dragon brains implanted into their brain. Both axioms and neurodonors can be users.
The Different Types of Cyborgs[]
Axioms, Rapunzels, Neurodonors, and Users are all cyborgs. But what differentiates them? When does an axiom become a neurodonor?
Neurodonors are entirely robotic except for their brain. Axioms have more than just a human brain; usually includes a human heart and chest.
The amount of an axiom that's robotic is referred to as their "percentage". A "high percentage" axiom is mostly robotic. High-percentage axioms and users run the highest risk of becoming Rapunzels.