Codependency describes the relationship between the abuser and the enabler. Both may have suffered childhood abuse, but this is not always the case - an abuser can wear down a healthy person's self-esteem over time, making them an enabler; but it is rare for an enabler to "create" an abuser out of a healty person.
Codependency can exist between partners, parents and children, boss and employee... pretty much any close relationship can develop into codependency. It is marked by enmeshment - the inability of the parties to experience individual emotions and actions separate from the relationship as the boundaries between individuals break down.
Normally, the abuser exhibits some destructive behavior and the enabler allows it to continue and, in some cases, even creates an environment that supports it. The enabler may be the victim of the abusive behavior, but this is not always the case - sometimes the "victim" of the destructive behavior is the abuser themselves or the children, etc. In some cases, both people are abusers and enablers of each other, and this is normally the hardest form of codependency to overcome.
Just a few examples:
The man who ignores his wife's mental issues, pretending she is normal or making the children responsible for her care, while she puts herself and the family at risk with her behavior.
The wife who makes excuses for her husband's drinking, blames herself for him beating her, and lies to family and friends about why she can't see them (i.e. child sick, rather than a black eye).
The son that defends his mother's abusive and inappropriate behavior toward his wife or girlfriend and will not listen to or support their complaints and concerns, who eventually gets rid of the woman questioning his mother's "love and devotion".
The daughter who must have her father's approval for all her life decisions, and will change her decisions to please him regardless of her husband's wishes or input or whether the decision is in the best interest of herself or her marriage.
The husband and wife who rationalize their drinking and drug abuse as "bonding", and constantly pull each other back into and reinforce the addiction.
These are just a few examples, but codependency can take on many forms. It is a relationship marked by an unhealthy lack of personal boundaries and emotional enmeshment. It is not the same as being interdependent - where two parties work together but each have their own thoughts, actions, emotions, and personality. In codependent relationships the parties are fused - their pattern of behaviors could not continue without the other person and the other person is seen as an extension of themselves.
It is better to be hated for what you are than to be loved for what you are not. --- Andre Gide
Selfishness is not living as one wishes to live, it is asking others to live as one wishes to live. --- Oscar Wilde