Definition 91.17.1. Let $A \to B$ be a ring map. Let $M$ be a $B$-module. The map $M \to L_{B/A} \otimes _ B^\mathbf {L} M[1]$ in (91.17.0.1) is called the Atiyah class of $M$.

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).