What does the term 'concave' refer to?

The term 'concave' specifically describes a shape that is rounded inward, resembling a cave or hollow area. This is in contrast to a convex shape, which bulges outward. In various contexts, such as geometry or optics, 'concave' surfaces or lenses curve inward, which can affect how light or objects interact with them. For example, concave mirrors are used in applications like reflective telescopes because they can focus light to a single point. This inward curvature is what distinguishes it from other forms like flat surfaces or angular shapes, which do not exhibit the same inward bending characteristic. Understanding the properties of concave shapes is essential in fields that involve design and physics, emphasizing their unique functional attributes.