Final answer:
A corner reflector returns light back exactly in the direction from which it came, utilizing total internal reflection, and is used in devices like binoculars and periscopes.
Step-by-step explanation:
The role of a corner reflector is to return light in the exact direction from which it originated. This is achieved by using an object with two mutually perpendicular reflecting surfaces, which allows for light that enters to be reflected back parallel to its original direction. When conditions for total internal reflection are met, which can occur with a critical angle of less than 45°, corner reflectors can be incredibly efficient. Such reflectors are employed in various optical devices, including binoculars and submarine periscopes, due to their ability to reflect 100% of the light that falls on them, unlike regular mirrors that may absorb some of the light.