Diagram

In category theory, a diagram is merely a suggestive term for a functor reflecting how $F$ is thought of as indexing a family of objects and morphisms in a category. Diagrams are used formalise commutative diagrams.

Definition

A diagram of type $𝐉$ in a category $𝐂$ is a functor $F:𝐉\to 𝐂$ from a small category called the index category or the scheme.[cite:@riehl2017category@wikipedia2024diagram]