Bip39 Mnemonic. The passphrase just isn't picked through the predefined list of 2048 words – it might be any word or phrase you decide on. BIP39 is actually a layout implementation that lays out how copyright wallets make the list of words (or "mnemonic codes") that make up a mnemonic https://bookmarkbooth.com/story19096186/bip-39-https-linktr-ee-bip39-top-guidelines-of-bip39-words