A mirage is an optical illusion where the image of some object appears displaced. It may be seen above, below or to the side of its true position. This is a result of spatial variation of the refraction of air, as the light is bent around the pockets of differing air temperatures. For that reason, mirages tend to be more common in the desert or at sea. The Fata Morgana, an illusionary island, is probably one of the most famous examples. In our area, the mirages tend to be less dramatic. Most common are areas on the road way that appear to be wet, but are actually dry.
Mary Knapp, Weather Data Library