A mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. The word comes to English via the French (se) mirer, from the Latin mirari, meaning "to look at, to wonder at".
An inferior mirage seen in the Mojave Desert in a Nevada spring
A hot-road mirage, in which "fake water" appears on the road, is the most commonly observed instance of an inferior mirage.
Heat haze seen through exhaust gas from a jet engine
Above: A superior mirage of a plane on ice, McMurdo Station Below: An artificial mirage, using sugar solutions to simulate the inversion layers.
Optical phenomena are any observable events that result from the interaction of light and matter.
A 22° halo around the Moon in Atherton, California
A solar halo as seen from 41° south latitude
A circumzenithal arc over Grand Forks, North Dakota
The Belt of Venus over Paranal Observatory atop Cerro Paranal in the Atacama Desert, northern Chile