The Stacks project

Definition 34.8.1. Let $T$ be an affine scheme. A standard ph covering is a family $\{ f_ j : U_ j \to T\} _{j = 1, \ldots , m}$ constructed from a proper surjective morphism $f : U \to T$ and an affine open covering $U = \bigcup _{j = 1, \ldots , m} U_ j$ by setting $f_ j = f|_{U_ j}$.