Passphrase (25th word)

A passphrase, often called the "25th word" or "13th word", is an optional extra word or phrase you can add to a seed phrase under the BIP39 standard. Combined with your 12 or 24 recovery words, it creates a completely different set of wallets. Without the exact passphrase, someone who finds your seed words sees only the original, passphrase-free wallet.

This adds protection against physical theft of your seed backup and allows "plausible deniability": you can keep a small balance in the standard wallet and the bulk behind the passphrase. Most hardware wallets, including Trezor, Ledger and Coldcard, support it.

The danger is that there is no reset. The passphrase is case-sensitive and every character matters; forgetting it, or a single typo, means the funds behind it are lost forever, and no company can recover them. If you use one, back it up separately from the seed phrase, test recovery with a small amount first, and make sure a trusted person could find both in an emergency.