An air gapped machine is simply one that cannot connect to any outside agents. From the highest level being the internet, to the lowest being an intranet or even bluetooth.

Air gapped machines are isolated from other computers, and are important for storing sensitive data or carrying out critical tasks that should be immune from outside interference. For example, a nuclear power plant should be operated from computers that are behind a full air gap. For the most part, real world air gapped computers are usually connected to some form of intranet in order to make data transfer and process execution easier. However, every connection increases the risk that outside actors will be able to penetrate the system.