Final answer:
A concave mirror is a curved mirror that curves inward and forms both real and virtual images. A concave lens is a diverging lens and only forms virtual images.
Step-by-step explanation:
A concave mirror is a curved mirror that curves inward, with its reflecting surface on the inner side of the curved surface. It is a converging mirror, meaning that light rays that strike it parallel to its axis converge at one or more points along the axis. This type of mirror can form both real and virtual images, depending on the position of the object relative to the focal point.
On the other hand, a concave lens is a diverging lens that causes light rays to bend away from its optical axis. The lens is thinner at the center and thicker at the edges. It is used to correct nearsightedness and can only form virtual images.