Catamorphism

https://en.wikipedia.org/wiki/Catamorphism

The concept of catamorphism (Greek: κατά "downwards") denotes the unique homomorphism from an initial algebra into some other algebra.

In FP, catamorphisms provide generalizations of folds of lists to arbitrary algebraic data types, which can be described as initial algebras. The dual concept is that of anamorphism that generalize unfolds.