noun /ˈkætəˌɡoɹi/
a) A group, often named or numbered, to which items are assigned based on similarity or defined criteria.
This steep and dangerous climb belongs to the most difficult category.
b) A collection of objects, together with a transitively closed collection of composable arrows between them, such that every object has an identity arrow.
I wouldnt put this book in the same category as the authors first novel.
Wikipedia foundation.