A natural transformation is a concept in category theory, a branch of mathematics. It describes a way to transform one functor into another while preserving the structure of the categories involved. Specifically, if you have two categories, C and D, and two functors, F and G, a natural transformation provides a systematic way to relate the outputs of these functors for every object in C. In simpler terms, a natural transformation consists of a collection of morphisms that connect the images of the functors. These morphisms must satisfy a specific condition called "naturality," which ensures that the transformation behaves consistently across the entire category. This concept is essential for understanding relationships between different mathematical structures.