Air-gapped

In addition to encrypting any sensitive e-mails, she began using different computers for editing film, for communicating and for reading sensitive documents (the one for sensitive documents is air-gapped, meaning it has never been connected to the Internet).

Source: wiktionary

In the past two years a group of researchers in Israel has become highly adept at stealing data from air-gapped computers—those machines prized by hackers that, for security reasons, are never connected to the internet or connected to other machines that are connected to the internet, making it difficult to extract data from them.

Source: wiktionary

It also appears that the controllers running the centrifuges were air gapped and not directly connected to the Internet.

Source: wiktionary

At least twice, [Dario] Amodei also used an air-gapped computer to write critical strategy documents, connecting the machine directly to a printer to circulate only physical copies. He was paranoid about state actors stealing OpenAI’s secrets and building their own powerful AI models for malicious purposes.

Source: wiktionary