Source : Free On-Line Dictionary of Computing

passphrase
     
         A string of words and characters that you
        type in to authenticate yourself.  Passphrases differ from
        passwords only in length.  Passwords are usually short - six
        to ten characters.  Passphrases are usually much longer - up
        to 100 characters or more.  Their greater length makes
        passphrases more secure.  Modern passphrases were invented by
        Sigmund N. Porter in 1982.
     
        Phil Zimmermann's popular encryption program {PGP}, for
        example, requires you to make up a passphrase that you then
        must enter whenever you sign or decrypt messages.
     
        {(http://world.std.com/~reinhold/diceware.page.html)}.
     
        (1996-12-21)