Wiktionary
n. (context computing English) A password that comprises a whole phrase.
Wikipedia
A passphrase is a sequence of words or other text used to control access to a computer system, program or data. A passphrase is similar to a password in usage, but is generally longer for added security. Passphrases are often used to control both access to, and operation of, cryptographic programs and systems. Passphrases are particularly applicable to systems that use the passphrase as an encryption key. The origin of the term is by analogy with password. The modern concept of passphrases is believed to have been invented by Sigmund N. Porter in 1982.
Usage examples of "passphrase".
Besides, all the guards would have to memorize the phrase, and any passphrase that included the word coward usually made the guards very conscious of not acting like one.