Bip39. The passphrase is not picked in the predefined list of 2048 words – it might be any word or phrase you decide on. BIP39 can be a style implementation that lays out how copyright wallets build the set of words (or "mnemonic codes") which make up a mnemonic sentence, https://altbookmark.com/story20266882/bip39-mnemonic-https-linktr-ee-bip39-the-basic-principles-of-bip39-mnemonic