Here's why:
* Multiple Books: There are many books in the Geronimo Stilton series, each with its own story.
* Shared Characters: The series features recurring characters like Geronimo Stilton, Thea Stilton, and Trap.
* Similar Style: The books all share a similar writing style, often with humorous elements and a focus on adventure.
So, while each individual Geronimo Stilton book can be considered a novel, the series as a whole is a collection of novels.