A retroreflector is a device or surface that reflects radiation back to its source with minimum scattering. This works at a wide range of angle of incidence, unlike a planar mirror, which does this only if the mirror is exactly perpendicular to the wave front, having a zero angle of incidence. Being directed, the retroflector's reflection is brighter than that of a diffuse reflector. Corner reflectors and cat's eye reflectors are the most used kinds.
A gold corner cube retroreflector
Eyeshine from retroreflectors of the transparent sphere type is clearly visible in this cat's eyes.
Bicycle retroreflectors
"Aura" around the shadow of a hot-air balloon, caused by retroreflection from dewdrops
A corner reflector is a retroreflector consisting of three mutually perpendicular, intersecting flat surfaces, which reflects waves directly towards the source, but translated. The three intersecting surfaces often have square shapes. Radar corner reflectors made of metal are used to reflect radio waves from radar sets. Optical corner reflectors, called corner cubes or cube corners, made of three-sided glass prisms, are used in surveying and laser ranging.
A corner reflector for radar testing
Octahedral corner reflector on the mast of a yacht.
A buoy in San Diego Bay with angled plates at the top.
Radar reflector on an abutment of a bridge