I though it meant two people dependent on each other emotionally and physically where one person is ill or an alcoholic and the other tries to fix them,change them, make the problem go away but is actually making the habits more entrenched.Like a woman who will not leave a violent,abusive, alcoholic husband and devotes her time and energy to make him better then ignores the very real problems she herself has if she does not have someone to mother or make better.Codependents,need someone to mother,take care off because they are terrified of focusing on themselves and their own problems.
These relationships happen between husband's and wives, mothers and daughters, fathers and daughters/sons etc