An "Open Set" is a concept in mathematics, particularly in topology. It refers to a collection of points in a space where, for every point in the set, there exists a surrounding area that also belongs to the set. This means that you can move a little in any direction from any point in the open set and still remain within the set. In practical terms, an open set can be visualized as a circle drawn on a plane, where all the points inside the circle are included, but the points on the boundary are not. This idea is essential in various fields, including analysis, geometry, and mathematical logic.