The medical definition of depression is that it is a Disorder characterized by sadness sever enough or persistent enough to interfere with function also charecterised by decreased or loss of interest in activities for a defined period of time.

According to Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition(DSM-IV))as classified by specific symptoms. There are mainly three types of depression:

1. Major depression.

2. Dysthymia.

3. Depressive disorder not otherwise specified.

Other Types of Depression As classified by causes are:

1. Depressive disorder due to a general physical condition.

2. Substance induced depressive disorder.