What is "heptalogy"

n. (context rare English) # A set of seven works of art that are connected, and that can be seen either as a single work or as seven individual works. They are commonly found in literature, film, or video games.

A heptalogy (from Greek ἑπτα- hepta-, "seven" and -λογία -logia, "discourse") is a compound literary or narrative work that is made up of seven distinct works. Whilst not in wide usage, it has been used to describe such examples as the Harry Potter series of books.