A cold wallet is generated on a trusted device or computer via an @airgap.If the device is to be reused, the data storage should be securely overwritten.As soon as a cold wallet is connected to the Internet or its mnemonic phrase or @spend-key is entered on an Internet-connected device, it's no longer "cold" and should be considered "hot".
A Monero @paper-wallet can be generated by downloading the source code of https://moneroaddress.org/.Verify the signature of the code on a trusted airgapped device.Create the wallet and print or store it on the media of your choice.
Monero accounts and paper-wallets can be stored on any media - paper, USB drive, CD/DVD, or a hardware wallet device (Ledger available since June 2018).