Major Depressive Disorder
Depression is the #1 reason why people get psychological counseling. However, there is a difference between feeling depressed and being clinically depressed. Major depressive disorder is classified as a mood disorder in which people have periods of hopelessness and sadness that last for more than 2 weeks and don't appear to have a specific cause (although this varies). This is more than "having the blues" but is a period of intense psychological pain that includes hopelessness, feeling worthless, loss of pleasure in things that previously were pleasurable, etc.