I think it's dandylion that I got this from, but my favorite definition of codependency is the "chronic neglect of Self".
It manifests in behaviors of all kinds across a massive spectrum, which to me sort of spider webs out into multiple directions in life & relationships. It's not linear or check-listable or balance-sheetable in terms of identifying or treating or correcting. Some people act codependently at times, others ARE codie to their core being.