Images are formed by lenses and mirrors when rays of light converge, or appear to converge.
A real image is one in which the rays of light converge on each other. That is to say, if you traced the path of light rays from the source through the lens (or mirror) the rays cross at a point. Real images are called "real" because one can place a screen at this location and actual see the image created on the screen; or one could say it is because the rays of light really cross.
A virtual image is one in which the rays of light do not actually converge to each other. That is if you trace the rays of light they do not cross at a point. However, if you look at the rays of light as they leave the lens (or mirror) they appear to come from a location opposite from the source. They appear to come from a location where light rays do not actually exist. Virtual images are called virtual because if you could put a screen where the image appears to be it would not appear on the screen (remember: there is not actually any rays of light there).
The image that is formed by the actual intersection of the reflected/refracted lights, is called a real image.Images produced due to a concave mirror are real except one condition i.e. when object is placed in between focus & optical centre.You can catch these images on a screen. Generally these are inverted, diminished in nature.
Contrary to this when the reflected/refracted lights diverge from each other, we get virtual image on the back side of the mirror, when the reflected/refracted lights are produced backward. These are erect & can't be caught on a screen.