General terms:
* Series: This is the most common and straightforward term.
* Saga: This emphasizes the epic scope and length of the story.
* Cycle: This implies a connected series of events or themes.
* Sequence: This focuses on the order of the books in the series.
More specific terms:
* Fantasy epic: This highlights the genre and grand scale of the story.
* High fantasy: This emphasizes the focus on magic, mythology, and other fantastical elements.
* Mythological series: This points to the creation of a new mythology within the series.
* Epic fantasy trilogy/tetraology: This specifies the genre and the number of books.
Ultimately, the best word to use depends on the specific context and the emphasis you want to convey.