air gap

noun3

1. •
   A network security measure that consists of ensuring that a secure computer network is physically isolated from unsecured networks, such as the public Internet or an unsecured local area network.

   • The structure and design of Stuxnet confirms the Iranian air gap, as the attackers clearly designed Stuxnet to jump an air gap utilizing multiple methods. — 2016
2. •
   A type of spark gap using a tube filled with air (which is mostly nitrogen), nitrogen alone, or other gases.
3. •
   A gap where there is a vacuum (not actually air), used to reduce power consumption in microelectronics.