My understanding of air-gapped network/computer is that it gets no access to Internet/External devices (like a thumb drive in this case). So is accurate to call it "hacking air-gapped network"?
In quite every system you need to exchange data, and the usage of a medium to move data between the trusted host and the untrusted host is _usually reasonable_ and _common practice_ (traditionally you move data from black to red with less restrictions, while the reverse procedure is more rigorous).
Making a comparison, I’d say air gapping is to networking what galvanic isolation is to circuits: you don’t have direct contact, but there’s information exchange (be it bytes or em fields).
EDIT: I would call a (strictly) isolated computer a tempest-compliant and physically isolated host.
Say you store your private PGP-key on a air-gapped computer. When receiving a sensitive document you put in on a USB-drive, enter it to the air-gapped machine and then physically destroy the USB-drive. The air-gapped machine then directly presents the decryption on a monitor.
There definitely exist scenarios where the air-gapped machine to not have to both communicate out and in, but where only in is required.
As others said, you usually need to move data. So, the typical solution for defense sector was to use high-assurance guards or data diodes. The former are like firewalls with an implementation designed to actually stop state-sponsored hackers rather than fill bank accounts keeping out the least skilled hackers. They do the latter, too, at the prices they charge. The data diodes are devices that allow data to only flow one way. There's at least two, use cases for that depending on which way the data flows.
Indeed, A and B are not "gapped" if a thumb drive connects to B, and then later the same thumb drive connects to A.
That's the same as being able to send a datagram from B to A over a network.
"Air gapped" is an idiotic term to begin with.
Radio communication such as Wi-Fi is literally air-gapped.
The plates of a capacitor can use air as a dielectric, making them literally air-gapped, yet the cap will pass AC signal, and two adjacent air-gapped inductors can pass signal, as well as power with great efficiency.
It's a perfectly reasonable term. It's not used for its literal meaning here, but that's fine. We use "network" to describe things that are not literally a net-like arrangement of threads, wires, etc.
