Definition 8.4.6.1. Let $\operatorname{\mathcal{D}}$ be a locally small $\infty $-category which admits small colimits. We say that an object $X \in \operatorname{\mathcal{D}}$ is atomic if the corepresentable functor
\[ h^{X}: \operatorname{\mathcal{D}}\rightarrow \operatorname{\mathcal{S}}\quad \quad Y \mapsto \operatorname{Hom}_{\operatorname{\mathcal{D}}}(X,Y) \]
preserves small colimits.