This article does not have any sources. (January 2012)
In psychology, depression is a mood where a person is very sad. Depression may also mean a person has learned helplessness or is not interested in anything. Depression that lasts a long time is called major depressive disorder. This can be a very serious mental illness, especially when not treated. If someone reaches extreme levels of depression it can make them have thoughts of suicide. This is called suicidalness, suicidality or suicidalism.