An image is said to be virtual when the reflected rays instead of meeting actually appear to meet and an image is said to be real when reflected rays actually meet.
The image formed on a flat or a plane mirror is said to be virtual because the reflected rays instead of meeting actually appear to meet. Also, one characteristic of every virtual image is that it always erect that means that they will be right side up.
But, real images are always inverted that means that they will be upside down.
Another characteristic of real images is that because the rays come together, the image can be projected onto a screen. If you held up a screen to a mirror, you wouldn't get an image. That's because the rays are diverging instead of converging.