What is "coden"

CODEN – according to ASTM standard E250 – is a six character, alphanumeric bibliographic code, that provides concise, unique and unambiguous identification of the titles of periodicals and non-serial publications from all subject areas.

CODEN became particularly common in the scientific community as a citation system for periodicals cited in technical and chemistry-related publications and as a search tool in many bibliographic catalogues.