[pjc50]

An airgapped system is one that's basically unusable because you can't communicate with other systems.

[AlexandrB]

Can't help but think back to my youth where nearly every system was airgapped, but were plenty usable regardless.

[mycall]

A system can be more than one computer, i.e. mainframe. Airgapped systems can include multiple computers that are disconnected from external networks. They can be very useful for specialized applications.