retrodirective mirror

retrodirective mirror

[¦re·tro·di′rek·tiv ′mir·ər]
(optics)
An optical system consisting of two mutually perpendicular plane mirrors; it reflects any beam of light which lies in a plane perpendicular to the mirrors into a direction antiparallel to its original direction.
An optical system consisting of three mutually perpendicular plane mirrors; it reflects any beam of light into a direction antiparallel to its original direction.