What is a series of 12 books called?

Could you please elaborate on the context in which this question arises? However, if I were to hazard a guess without further details, a series of 12 books is typically referred to as a "book series" or "series of books." It implies a collection of works that are interconnected in some way, often sharing a common theme, characters, or plotline. The individual books within the series are usually numbered or titled in a way that indicates their order within the series. But again, the exact terminology and context might vary depending on the type of books or the intended audience.