Bip39 Checksum. Push X to abort passphrase software and retain modifying the passphrase. Picking CANCEL after an abort will prevent the process. BIP39 is actually a design and style implementation that lays out how copyright wallets build the list of words (or "mnemonic codes") which make up a mnemonic sentence, https://bookmark-dofollow.com/story23367390/bip-39-https-linktr-ee-bip39-the-2-minute-rule-for-bip39-word-list