Security through obscurity would be having a system connected to a network, but relying on a secret / unknown protocol to secure it.

Air-gapping a system is a real and very useful security method. That being said, it's not enough by itself.

If you're interested, have a look at past examples, like the recent work on breaking Tetra communication standard and Stuxnet.

That's why I only communicate via poop/sparkle emoji Morse code

✨💩💩💩 ✨✨💩 ✨✨✨ 💩➿✨💩✨✨ ✨✨ 💩✨💩 ✨➿💩 ✨✨✨✨ ✨✨ ✨✨✨

Security by obsolescence