An Air Gap is a Bitcoin wallet system with a two-device procedure, in which one of the devices (the one that contains the private key generation and information) is always kept without an internet connection. This ensures the most security for your keys as it ‘gaps’ the wallet from the rest of the world. This device would then communicate through Transaction signing onto the secondary device, which will be broadcast to the rest of the Bitcoin network. This is the preferred method of cold storage for Bitcoin, and is used by many hardware wallets.