Passphrase (secret password) is an advanced feature that adds a layer of security to your cryptocurrency account. This feature is only recommended for users with advanced knowledge, applicable to both Ledger Nano X and < cold wallets a i=4>Ledger Nano S Plus.
Please read this article carefully and watch the video before doing it.
Security tips
The 24-word recovery string and passphrase allow for more professional security of your cold wallet cryptocurrency accounts. But if you are not very technical, storing the recovery chain safely is the best security method. Adding a passphrase (from the 25th word) will be more secure but also complicates the problem and is not too necessary. If you forget your passphrase after installation, you will not be able to recover your coins even if you have all 24 words. Be serious!