Depression, in psychology, a mood or emotional state that is marked by feelings of low self-worth or guilt and a reduced ability to enjoy life. A person who is depressed usually experiences several of the following symptoms: feelings of sadness, hopelessness, or pessimism; lowered self-esteem and heightened self-depreciation; a decrease or loss of ability to take pleasure in ordinary activities; reduced energy and vitality; slowness of thought or action; loss of appetite; and disturbed sleep or insomnia. Depression differs from simple grief or mourning, which are appropriate emotional responses to the loss of loved persons or objects. Where there are clear grounds for a person’s unhappiness, depression is considered to be present if the depressed mood is disproportionately long or severe vis-à-vis the precipitating event. The distinctions between the duration of depression, the circumstances under which it arises, and certain other characteristics underlie the classification of depression into different types. The three main types are bipolar disorder, major depressive disorder (clinical depression), and persistent depressive disorder. - Britannica, 2015

Dewey Number

  • Mental and emotional illness = 363.2
  • Depression = 362.28
  • Diseases of the nervous system and mental disorders = 616.8
  • Suicide = 362.28

Keyword Searching

  • Bipolar disorder

Subject Headings


  • Issues in Society - Volume 303 - Understanding mental illness - 2010
  • Issues - Number 80 - Mental Health - 2010