Depression is an uncomfortable mental state that may be characterized by such adjectives as blue, dejected, or discouraged.
In ordinary usage the word refers to a mood state that in medicine is called dysthemia, as contrasted with the normal state, euthymia, and the opposite state, elation. In psychiatric usage, disorders of mood are called affective or mood disorders.
Depression may be this in itself or a symptom of another mental disorder. Normal human responses to some situations may also include transient depressions. For example, mourning usually involves a depressed mood, but this is considered to be an expected response to loss.
Major depressions occur in 10-20% of the world's
population in the course of a lifetime. Women are more often affected than men, by a two-to-one ratio, but cultural and social rather than biological factors primarily account for this difference. Relatives of patients with major depression seem at some higher risk of becoming depressed, and about 2% of the population may have a chronic disorder known as a depressive personality. (The conditions called bipolar disorder, dysthemic disorder, cyclothymic disorder, and substance-induced mood disorders also involve periods of depression.)