open set

This term is a technical primitive in topology and mathematical analysis. It describes a region where every point is an interior point, meaning there is always a small amount of "breathing room" around any point within the set that remains inside the set. This distinguishes it from a closed set, which contains all its boundary points.

In practical application, an open set is often visualized as a region without its boundary. For example, in a standard 2D plane, the interior of a circle without the edge itself is an open set. Because it is a specialized mathematical term, it is used almost exclusively in formal academic or professional contexts within mathematics and physics.