A "concave" shape curves inward, resembling the inside of a bowl or a cave. In geometry, a concave polygon has at least one interior angle greater than 180 degrees, causing it to bend inward. This contrasts with a "convex" shape, which bulges outward. Concave mirrors, often used in telescopes and makeup mirrors, reflect light inward to a focal point. This property makes them useful for focusing light and creating magnified images. Similarly, concave lenses are thinner in the center and can diverge light rays, which is important in various optical devices like glasses and cameras.