What is a concave lens?

A concave lens is characterized by being thinner at the center than at the edges. This shape allows it to diverge light rays that pass through it. When parallel light rays enter a concave lens, they spread out or diverge, which means they appear to originate from a point behind the lens known as the focal point. This is a key property of concave lenses, often used in various optical devices such as glasses for nearsightedness, in cameras, and in scientific instruments because they help to form virtual images that can be magnified.

The other choices describe different types of lenses or their functions; a lens that is thicker in the center than at the edges is a convex lens, which converges light rays. A lens that focuses light into a real image also refers to a convex lens, which can converge light to form real images. Therefore, option C accurately describes a concave lens and its distinct characteristics.