A transformation1 $\smash {\alpha \colon F\Rightarrow G}$ from $F$ to $G$ is a collection
\[ \webleft\{ \alpha _{A}\colon F\webleft (A\webright )\to G\webleft (A\webright )\webright\} _{A\in \text{Obj}\webleft (\mathcal{C}\webright )} \]
of morphisms of $\mathcal{D}$.
1Further Terminology: Also called an unnatural transformation for emphasis.
