Depressive disorders come in different forms. There are several different diagnoses for depression, mostly determined by the intensity of the symptoms, the duration of the symptoms, and the specific cause of the symptoms, if that is known
The following three different kinds of depression are distinct depressive disorders described in the DSM. A common criteria is that their symptoms either cause 1) significant distress or 2) impair one’s functioning (e.g. work, school, relationships). Also, these depressive symptoms are not caused by a medical condition or substance (e.g. medication, drug).
1) Major Depression - This is the most serious type of depression, in terms of number of symptoms and severity of symptoms, but there are significant individual differences in the symptoms and severity. You do not need to feel suicidal to have a major depression, and you do not need to have a history of hospitalizations either, although both of these factors are present in some people with major depression. There is no official diagnosis of "moderate depression."
2) Dysthymic Depression - This refers to a low to moderate level of depression that persists for at least two years, and often longer. While the symptoms are not as severe as a major depression, they are more enduring and resistant to treatment. Some people with dysthymia develop a major depression at some time during the course of their depression.
3) Bipolar Depression - This type includes both high and low mood swings, as well as a variety of other significant symptoms not present in other depressions.