Definition: A passphrase is a series of two or more words or a combination of words and special characters. Passphrases are used for encryption.
A string of words and special characters create a robust mans of granting access to infrastructure owners. A complex expression can be an effective instrument for controlling access to your information system or that of your organization. A multi-word authentication expression is more convenient to remember and much more robust. The more words you use the harder the cracker has to work to break into your system.
Its Relevance: Remembering the words to be used to gain access to an information system can be inconvenient. A string that consists of more than one word (that possibly contains special characters) might be easier to remember and harder to crack. Users should be certain, however, that they avoid using well known or common phrases such as "a hard day's night", etc.
Pass phrases, regardless, are much harder for nefarious attackers to crack. A good string of words that have meaning to you are easier to remember.