The Stacks project

Definition 76.47.1. Let $S$ be a scheme. Let $f : X \to Y$ be a morphism of algebraic spaces over $S$.

1. We say $f$ is perfect if the equivalent conditions of Morphisms of Spaces, Lemma 67.22.1 hold with $\mathcal{P} =$“perfect”.

2. Let $x \in |X|$. We say $f$ is perfect at $x$ if there exists an open neighbourhood $X' \subset X$ of $x$ such that $f|_{X'} : X' \to Y$ is perfect.