Bip39 Checksum. The passphrase will not be chosen from the predefined list of 2048 words – it could be any word or phrase you choose. Any person else who discovers the phrase can steal the bitcoins. It has to be kept top secret, as an example it should not be https://socialbaskets.com/story4628253/bip39-passphrase-https-linktr-ee-bip39-a-review-of-bip39-words