The Stacks project

Definition 34.6.5. Let $T$ be an affine scheme. A standard syntomic covering of $T$ is a family $\{ f_ j : U_ j \to T\} _{j = 1, \ldots , m}$ with each $U_ j$ is affine, $U_ j \to T$ standard syntomic and $T = \bigcup f_ j(U_ j)$.