Cosmic Optical Background (COB) radiation is the Visible Light analog to Cosmic Microwave Background, in the sense of there being optical signal detected in areas between the known sources. As such, it is a portion of the Cosmic Background Radiation.
Milky Way sources are considered something separate, so the study of COB is hampered by the existence of the Milky Way's Diffuse Galactic Light (DGL).
Since visible light is actually a very narrow band, the sources of COB are generally extensions of sources of Infrared and/or Ultraviolet, so the term COB is perhaps most often used and discussed regarding its effect on observation in the visible range.
Cosmic Background Radiation (CBR)
Extragalactic Background Light (EBL)