Bip39 Seed. The passphrase is not really chosen within the predefined list of 2048 words – it may be any word or phrase you select. BIP39 is really a design implementation that lays out how copyright wallets produce the list of words (or "mnemonic codes") which make up a mnemonic https://socialislife.com/story4512305/bip39-wallets-https-linktr-ee-bip39-a-simple-key-for-bip39-unveiled