Bip39 Vs Slip39. The passphrase just isn't selected in the predefined list of 2048 words – it may be any word or phrase you choose. BIP39 is a structure implementation that lays out how copyright wallets make the list of words (or "mnemonic codes") which make up a mnemonic sentence, https://socialwoot.com/story20519561/bip39-list-https-linktr-ee-bip39-bip-39-no-further-a-mystery