With a passphrase, someone who finds your 24 words still sees only an empty or decoy wallet. It is strong protection — but if you forget the passphrase, the funds behind it are gone. Back it up separately from the seed phrase.
Wallets & security
Passphrase (25th word)
Also called: 25th word · BIP39 passphrase
In shortAn optional extra word added to a seed phrase that opens a completely separate, hidden wallet.