Original: Major depressive disorder ( MDD ) ( also known as recurrent depressive disorder , clinical depression , major depression , unipolar depression , or unipolar disorder ) is a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem , and by loss of interest or pleasure in normally enjoyable activities .
Simplified: Major depressive disorder is also referred to as major , biochemical , clinical , endogenous , or biological depression . It may also be called unipolar affective disorder .