What is the DSM and how is it used to diagnose psychological disorders?

The Diagnostic and Statistical Manual of Mental Disorders, or DSM, published by the American Psychiatric Association, is the standard classification system for diagnosing psychological disorders in the United States. The current edition is the DSM-5-TR. It defines each disorder by specific diagnostic criteria including required symptoms, duration, and functional impairment. A diagnosis requires that symptoms cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.