The past perfect continuous tense is used to describe an action that had happened continuously in the past, until another past event took place. It is also known as the past perfect progressive tense. Some synonyms for this tense include the past perfect continuous verb tense, the past perfect progressive verb tense and the pluperfect continuous tense. It is an essential tense used in storytelling to describe events that had been happening for a while before something else happened. The past perfect continuous describes a past event that was ongoing at a particular time in the past, and it helps add depth and detail to a narrative.