Past Perfect Continuous Tense
The past perfect continuous tense (also known as the past perfect progressive tense) shows that an action that started in the past continued up until another time in the past. The past perfect continuous tense is constructed using had been + the verb’s present participle (root + -ing).
Unlike the present perfect continuous, which indicates an action that began in the past and continued up to the present, the past perfect continuous is a verb tense that indicates something that began in the past, continued in the past, and also ended at a defined point in the past.
When, for, since, and before are words that you may see used alongside the past perfect continuous tense.