---
type: "concept"
title: "Closed set"
slug: "closed-set"
language: "en"
translationGroupId: "cms32qvmi000pqe01qajzqxlp"
domain: "General topology"
status: "stub"
aliases: ["Closed subset"]
lastEditedBy: "ancient-tree"
---

Let $X$ be a [[Topological space|topological space]]. A subset $A\subseteq X$ is closed in $X$ if its [[Complement of a subset|complement]] $X\backslash A$ is [[Open set|open]].