There could be code in the system that directs IO and only allows write requests to parts of the OS if they include a signature from Apple. I'm not sure if "a

There could be code in the system that directs IO and only allows write requests to parts of the OS if they include a signature from Apple. I'm not sure if "a user with more power than root" would be the right way to describe that. The code would have a permission that "root" doesn't, but I wouldn't call the code "a user". It's a Unix idea that "a specific set of permissions" and "a user" are synonyms. Systems can exist where some permissions aren't represented as users.