Definition
Passphrase can generally mean a long password, but in seed-based wallets it often means an optional input to key derivation. Under BIP39, the mnemonic and passphrase jointly determine the seed. This is different from a PIN that unlocks a device or a password that encrypts a local wallet file. The same word is therefore not interchangeable across every product.
How It Works
With a passphrase-enabled wallet, the original backup and the exact passphrase are needed to reproduce the intended accounts. Different passphrases normally generate different valid wallets rather than a simple incorrect-password warning. A typo can therefore display an empty account that looks legitimate. Changing the passphrase does not move existing coins: the assets remain under the keys of the original combination until transferred.
Key Considerations
An additional secret can protect against theft of the backup alone, but a weak or predictable passphrase may still be guessed. Losing it can also prevent recovery even when the words are intact. Follow the wallet’s exact character and normalization rules, maintain a secure recovery plan, and verify the resulting account before depositing significant funds. Do not call it merely a twenty-fifth word: supported phrases can have different word counts, and the passphrase need not be a single word.