Virtual Image
An optical image formed where light rays appear to diverge from, but do not actually intersect; cannot be projected on a screen.
Governing formula
v < 0 (for virtual image), m > 0 (upright)
SI unit
m
In depth
Virtual images are always upright. Formed by plane mirrors, convex mirrors, concave lenses, or convex lenses when object is within focal length ($u < f$).
Examples in the real world
Your upright reflection in a flat bathroom mirror or magnifying glass image.