Concave lenses are optical devices that are thinner in the center than at the edges. They diverge light rays that pass through them, causing the rays to spread out. This property makes concave lenses useful in various applications, such as in eyeglasses for correcting nearsightedness, where they help focus images correctly on the retina. These lenses are shaped like a bowl, curving inward, which is why they are called "concave." They can also be found in devices like cameras and projectors, where they help to create a wider field of view or to focus light in specific ways.