A catadioptric or retro-reflective system involves both catoptrics (the laws of light reflection) and dioptrics (the laws of refraction).
A catadioptric objective is composed both of mirrors (usually concave) and lenses. There are several families of this type of telescope: Cassegrain, Schmidt-Cassegrain, Maksutov, Ritchey-Chretien. The main advantage is that they provide a longer focal length than the tube or, for the same focal length, a more compact instrument.
A retro-reflector usually denotes the reflecting system fitted to vehicles, composed of a multitude of small lenses applied to a mirror. It reflects the light more or less in the direction it came from.