Bip39 Checksum. The passphrase isn't picked in the predefined list of 2048 words – it may be any word or phrase you select. BIP39 specifies a list of 2048 words from which the mnemonic phrase is picked out. Each and every word signifies a range inside of a binary sequence, https://bookmarklinking.com/story5589900/bip39-word-list-pdf-https-linktr-ee-bip39-bip39-words-an-overview