Past Perfect Continuous Tense is a tense used to talk about an action that started in the past and continued up until another time in the past. It is used to emphasize the continuity of an action that was in progress before another action in the past. It is formed with "had been + verb + -ing" and is used with time expressions such as when, before, by the time, for, since, and how long. Stative verbs cannot be used in this tense.