virtual image: an image for which the light does not pass through the position of the image; light appears to come from the position of a virtual image but does not pass through that position; a virtual image may be viewed or seen with the eye but it can not be projected onto a screen.

magnification: the ratio of the size of the image divided by the size of the object

concave: the inside of a curved mirror; also called a converging or positive mirror

convex: the outside of a curved mirror; also called a diverging or positive mirror

optic axis: the axis of symmetry for a mirror or a lens

converging: a mirror or lens that focuses incoming, parallel rays of light to a point; also called a positive mirror or lens

diverging: a mirror or lens that causes incoming, parallel rays of light to a leave the mirror or lens diverging or going away from each other and looking as if they had originated from a point; also called a negative mirror or lens

focal point: the point at which a converging mirror or lens focuses all the incoming, parallel rays of light; the point from which all the incoming, parallel rays of light appear to have gone through after interacting with a diverging mirror or lens

focal length: the distance from a mirror or lens to the focal point

principal rays: three representative rays that are used to locate and characterize the image because they are easy to draw or to understand.