A virtual image is produced by a concave mirror when the object is placed inside the focal length of the mirror. The image is located behind the mirror so you cannot touch it (that is why it is called virtual). It is easy to recognize virtual images with your eyes because they are upright.
In a concave mirror, the image is real if the distance of the object from the mirror is greater than the focal length and virtual if it is less than the focal length. If the object is at the focus the image is formed at infinity. In a convex mirror, the image is always virtual.
A concave mirror converges light; a convex one diverges it. The two faces of a lens may be concave or convex or plane, so it is better to class them also as converging or diverging lenses (see below)
With a converging mirror or lens, you get a real image of a real object placed further than one focal length from the mirror/lens. If it is closer than one focal length, then the image is virtual. The image of a real object in a diverging lens or mirror is always virtual.
