Automatic psychological process that protects the individual against anxiety and from awareness of internal or external stressors or dangers.
Defense mechanisms mediate the individual's reaction to emotional conflicts and external stressors.
Some defense mechanisms (e.g., projection, splitting, and acting out) are almost invariably maladaptive.
Others (e.g., suppression, denial) may be either adaptive or maladaptive, depending on their severity, inflexibility, and the context in which their occur.

American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. Fifth Edition. Washington, DC. American Psychiatric Association. 2013. p. 844.