An important characteristic of Bipolar disorder is that it includes :

Both Mania and depression

Bipolar I disorder involves both mania and depression, which are alternately present and sometimes interrupted by periods of normal mood. Manic episodes rarely appear by themselves; they usually alternate with depression. Bipolar mood disorders were earlier referred to as manic-depressive disorders. Some examples of types of bipolar and related disorders include Bipolar I Disorder, Bipolar II disorder and Cyclothymic Disorder.