The Stacks project

Definition 22.8.2. Let $(A, \text{d})$ be a differential graded algebra.

1. If $0 \to K \to L \to M \to 0$ is an admissible short exact sequence of differential graded $A$-modules, then the triangle associated to $0 \to K \to L \to M \to 0$ is the triangle (22.8.1.1) of $K(\text{Mod}_{(A, \text{d})})$.

2. A triangle of $K(\text{Mod}_{(A, \text{d})})$ is called a distinguished triangle if it is isomorphic to a triangle associated to an admissible short exact sequence of differential graded $A$-modules.