Meaning of PAST PERFECT in English

PAST PERFECT

ˌpast ˈperfect BrE AmE noun [singular] technical

the form of a verb that shows that the action described by the verb was completed before a particular time in the past, formed in English with ‘had’ and a past participle

—past perfect adjective

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.