noun
: node ; especially : either of two points so located on the axis of a lens or optical system that any incident ray directed through one will produce a parallel emergent ray directed through the other
noun
: node ; especially : either of two points so located on the axis of a lens or optical system that any incident ray directed through one will produce a parallel emergent ray directed through the other
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012