A mirage is the optical phenomenon that can make distant objects appear displaced, stretched, or duplicated over hot surfaces.
Mirages form when light travels through layers of air at different temperatures and densities. A hot road or desert surface warms the air immediately above it, creating a strong vertical temperature gradient. Light bends as it passes through these layers, so the eye traces the ray backward along a misleading path.
The familiar inferior mirage can make the sky appear like water on a distant road. Superior mirages occur when colder, denser air lies below warmer air and can make objects seem elevated. Complex temperature layers can produce looming or multiple images.
A mirage is not a hallucination or a reflection from actual water. It is a real light pattern produced by atmospheric refraction. The same physics explains some unusual views of ships, coastlines, and distant islands.