closed surface

A closed surface is a continuous, unbroken boundary that fully encloses a three-dimensional space, without any gaps or edges. Examples include the surface of a sphere, a cube, or a ball. It separates the inside (the enclosed volume) from the outside, allowing us to distinguish what is contained within from what is outside. Closed surfaces are fundamental in geometry and physics because they help describe shapes and regions where concepts like volume and surface area are well-defined. They are essential for understanding how objects and spaces are structured and behave in the physical world.