Your PIN prevents unauthorized users from reviewing balances and doing transactions. Your recovery sentence is an encoded version of your private key using normal dictionary words. This sentence should be kept secret: anyone knowing it can easily get access to your bitcoins. Your passphrase is an additional word appended to your recovery sentence that is never stored on your KeepKey. We do not recommend using the passphrase feature unless you completely understand the consequences in using it. Contact support for instructions on adding a passphrase.