Mirages are natural illusions that happen because of bending light rays that in turn creates a shifted image in the distance or sky. There are types of mirages like the inferior mirage which the observer sees bluish land that looks like water. Inferior mirages happen because light rays from the sky or the object travel the same air layers and bend the same amount too. Heat haze is an inferior mirage and happens you see objects through layer of heat gas or air often happening on the road. Superior mirages occur when there's a cooler level of air lower than a warmer level of air, on polar areas or icy landscapes.
Sorry it's a bit wordy :)