The 25th word (the Passphrase) feature is an advanced feature that allows you to generate a completely new private key by adding a 25th word to the existing 24 recovery words (mnemonic code) generated on your Biometric Wallet.
This means that even if your 24 recovery words are compromised or lost, you will only be able to recover your wallet if you know the 25th recovery word. You can set the 25th word to your own word, including numbers or alphabets, up to 8 characters long.
Please note that if you set the 25th recovery word while you are already using the Biometric Wallet, a new private key will be generated which replaces the existing private key, and you will not be able to access your existing assets.
(To access your existing assets, you will need to initialize your wallet and restore it with the 24 recovery words you previously stored.)
Furthermore, if you want to recover your wallet with the 25th word, you should recover with the 24 recovery words (mnemonic code) first.
After that, you can go to “Settings > Security > 25th Word” of the Biometric Wallet, you can put all the 24 recovery words and put the 25th word that you set before.
Also, this setting is an advanced feature, so you do not necessarily need to use the 25th word feature. Please choose carefully.