Pentalogy
A pentalogy (from Greek πεντα- penta-, "five" and -λογία -logia, "discourse") is a compound literary or narrative work that is explicitly divided into five parts. Although modern use of the word implies both that the parts are reasonably self-contained and that the structure was intended by the author, historically, neither was necessarily true: in fact, a pentalogia could be assembled by a later editor, just as Plotinus's Enneads were arranged in nines by Porphyry in order to create an overarching structure of six which would express the idea of perfection.