The Stacks project

Definition 13.10.1. Let $\mathcal{A}$ be an additive category. A triangle $(X, Y, Z, f, g, h)$ of $K(\mathcal{A})$ is called a distinguished triangle of $K(\mathcal{A})$ if it is isomorphic to the triangle associated to a termwise split exact sequence of complexes, see Definition 13.9.9. Same definition for $K^{+}(\mathcal{A})$, $K^{-}(\mathcal{A})$, and $K^ b(\mathcal{A})$.