I have been familiar with the term 'ghost (ring) peep sight" since the 70's, when referring to peep sights with small diameter outlines & larger diameter apertures whereas the ring around the outside is thin enough, to appear "ghostly", barely there, but it works to align your eye with the rear sight, if installed as well. Otherwise, it acts like a hunting rifle's peep sight that does not obscure the background from vision, due to having both eyes open - one eye sees the post or aperture inside the ring while the other eye sees just the target.