The point at which light rays passing through a convex lens or reflecting off a concave mirror converge. Parallel light rays incident on different points of a curved mirror are reflected at different angles. Similarly, rays passing through different parts of the lens are refracted at different angles. In the case of a concave mirror or convex lens, all the rays intersect at a single point, called the focal point. In solar energy, concave mirrors are often used, which concentrate the sun’s radiation into a focal point to heat the heat transfer medium.