Bip39 Checksum. The passphrase will not be selected with the predefined list of 2048 words – it could be any word or phrase you choose. And you should have penned it down in case you ended up hoping to keep an alternative open up to restore your accounts. Security from https://travialist.com/story9363742/bip39-https-linktr-ee-bip39-5-essential-elements-for-bip39-word-list