The pluperfect, often called the past perfect in English, is a verb tense that refers to an action that was completed at some point before the present time. It is a combination of the perfect tense and the simple past tense. The construction of the pluperfect in English is "had" plus the past participle, for instance, "had eaten."
The word "pluperfect" comes from the Latin meaning "more than perfect." In grammatical terms, "perfect" means "complete," so the pluperfect tense indicates that something is not only complete, but that it has been completed for some time. A sentence with the pluperfect often refers to two different events, one of them having been completed before the other occurred. For example, "The cat had eaten three koi before the caretaker chased it away from the pond" contains the pluperfect "had eaten" and the simple past "chased." This shows that the cat had finished eating three koi before another specified point in the past — the point when the caretaker chased it away.
The pluperfect tense has slight variations from either the simple past or the present perfect tense. The sentence "The cat had eaten three koi before the caretaker chases it away from the pond" contains two different events, but one event — the cat eating the koi — happened before the event happening in the present — the caretaker chasing it away. "Had eaten," in this example, is the present perfect tense, meaning that it reached completion before the present time, instead of before some point in the past. On the other hand, "The cat ate three koi" is in the simple past tense, meaning that it does not explicitly reference when it happened in relation to any other event, only that it happened sometime in the past.
Meaning of the pluperfect tense is fairly consistent among Indo-European languages, although of course its construction varies. Most often, however, the construction of the pluperfect is a combination of the perfect with the simple past. French, on the other hand, uses the construction avoir or etre plus participle as a simple past tense instead of as a perfect, but the pluperfect is still formed with the past tense of avoir or etre plus participle as in English. Koine and other ancient Greek dialects use a reduplication — an initial consonant plus "e" — to indicate completion, combined with a vowel change in the ending to indicate the past.