noun
: the cusped surface of maximum brightness that is sometimes observed when light is refracted or reflected by a curved mirror or interface and is geometrically the envelope of the system of refracted or reflected rays
noun
: the cusped surface of maximum brightness that is sometimes observed when light is refracted or reflected by a curved mirror or interface and is geometrically the envelope of the system of refracted or reflected rays
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012