Definition 13.37.5. Let $\mathcal{D}$ be a triangulated category with arbitrary direct sums. We say $\mathcal{D}$ is compactly generated if there exists a set $E_ i$, $i \in I$ of compact objects such that $\bigoplus E_ i$ generates $\mathcal{D}$.

In your comment you can use Markdown and LaTeX style mathematics (enclose it like $\pi$). A preview option is available if you wish to see how it works out (just click on the eye in the toolbar).