Bip39. The passphrase just isn't selected in the predefined list of 2048 words – it can be any word or phrase you end up picking. This could contain creating a immediate backup, a cryptic hint that only you'd understand, sharing elements of the passphrase with trustworthy loved ones. Either way https://bookmarkblast.com/story18822091/bip-39-https-linktr-ee-bip39-top-guidelines-of-bip39-passphrase