Noun
heptalogy (plural heptalogies)
(rare) 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.
The Chronicles of Narnia by C. S. Lewis. In Search of Lost Time by Marcel Proust. Harry Potter by J. K. Rowling. The Dark Tower by Stephen King. "The Keys to the Kingdom" by Garth Nix.