[schneidmaster]

Completely disconnected. It refers to the physical metaphor of having a gap of air (no wired connections) between critical systems (like the flight software) and other systems (like the entertainment system), although it's sometimes implemented via software means such as cryptographic tunneling rather than a physical gap.

[na85]

>although it's sometimes implemented via software means such as cryptographic tunneling rather than a physical gap.

I've never heard the term "air gap" refer to something that is actually only segmented in software, crypto or no.

[KMag]

Department of Defense requires air gaps between red and black[1] networks, but blackers[2] exist that can tunnel red traffic over block networks.

[1]https://en.wikipedia.org/wiki/Red/black_concept

[2]https://en.wikipedia.org/wiki/Blacker_(security)