# Closed set

## Complement of an open subset / From Wikipedia, the free encyclopedia

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In geometry, topology, and related branches of mathematics, a **closed set** is a set whose complement is an open set.[1][2] In a topological space, a closed set can be defined as a set which contains all its limit points. In a complete metric space, a closed set is a set which is closed under the limit operation.
This should not be confused with a closed manifold.