Closed immersion

In algebraic geometry, a closed immersion of schemes is a morphism of schemes ${\displaystyle f:Z\to X}$ that identifies Z as a closed subset of X such that regular functions on Z can be extended locally to X. The latter condition can be formalized by saying that ${\displaystyle f^{\#}:{\mathcal {O}}_{X}\rightarrow f_{\ast }{\mathcal {O}}_{Z}}$ is surjective.

An example is the inclusion map ${\displaystyle \operatorname {Spec} (R/I)\to \operatorname {Spec} (R)}$ induced by the canonical map ${\displaystyle R\to R/I}$.

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Wikipedia