There are multiple definitions of defense mechanism based on different theories. Generally, defense mechanisms are human responses responses to anxiety and how the consciousness and unconscious manage the stress of a social situation. Some of the most common defense mechanisms include:

Repression: forcing a feeling from the consciousness to the unconscious because it is seen as socially unacceptable

Regression: falling back into an early state of mental/physical development seen as less demanding and safer

Projection: possessing a feeling that is deemed as socially unacceptable and instead of facing it, that feeling or "unconscious urge" is seen in the actions of other people

Reaction formation: acting the opposite way that the unconscious instructs a person to behave, "often exaggerated and obsessive". For example, if a wife is infatuated with a man who is not her husband, reaction formation may cause her to – rather than cheat – become obsessed with showing her husband signs of love and affection.

Sublimation: seen as the most acceptable of the mechanisms, an expression of anxiety in socially acceptable ways