Past perfect is a tense that shows that an event happened prior to another event. For example you drove once when you were twelve years old, but didn't get your license until you were sixteen. http://www.ego4u.com/en/business-english/grammar/past-perfect http://www.englishtenses.com/tenses/past_perfect http://www.englishclub.com/grammar/verb-tenses_past-perfect.htm