The item being referred to is a method of storing private keys on a separate device to lower the risk of hacking. This method is called "cold storage" and involves storing private keys offline on a separate device, such as a hardware wallet, USB token, or paper wallet. By keeping private keys offline, the risk of hacking is minimized since the keys are not connected to the internet and cannot be accessed remotely. Cold storage is considered the safest way to store private keys, and it is recommended to use noncustodial cold storage until you are going to use the keys. When using cold storage, it is important to follow best practices like strong passwords, regular backups, and encryption to enhance security. Ultimately, there is no one wallet solution that is 100% unhackable, but hardware wallets coupled with extra security precautions, security features, and best practices offer a strong solution.