Depression is a mood disorder that causes a persistent feeling of sadness and loss of interest. Also called major depressive disorder or clinical depression, it affects how you feel, think and behave and can lead to a variety of emotional and physical problems. You may have trouble doing normal day-to-day activities, and sometimes you may feel as if life isn't worth living.
Major depressive disorder, is the main type of depressive disorder. When episodes of major depression are chronic and recurring, the condition is called persistent depressive disorder. Other types of depressive disorders include premenstrual depressive disorder, substance- or medication-induced depressive disorder, and depressive disorder due to another medical condition.