The Stacks project

Definition 98.12.1. Let $S$ be a locally Noetherian scheme. Let $p : \mathcal{X} \to (\mathit{Sch}/S)_{fppf}$ be a category fibred in groupoids. Let $\xi = (R, \xi _ n, f_ n)$ be a formal object. Set $k = R/\mathfrak m$ and $x_0 = \xi _1$. We will say that $\xi$ is versal if $\xi$ as a formal object of $\mathcal{F}_{\mathcal{X}, k, x_0}$ (Remark 98.9.2) is versal in the sense of Formal Deformation Theory, Definition 90.8.9.