Bipolar Disorder refers to a a mood disorder characterized by severe alterations in mood which are usually episodic and recurrent.
At least one mood episode must be of the "manic” type, in which a person experiences either extreme elevation in mood (euphoria) and energy level, or extreme agitation and irritability. In addition, episodes of depressed mood are usually present. Formerly called "Manic-Depressive Illness
Other /More definition:
Bipolar disorder or BP refers to a mood disorder involving manic episodes - intense and very disruptive experiences of heightened mood, possibly alternating with major depressive episodes; a mood disorder characterized by alternating periods of depression and mania. Moreover, Bipolar disorder refers to a psychological disorder characterized by extreme fluctuations in mood; . condition in which a person alternates between the two (2) poles of mania and depression; a major mood disorder with a distinct period during which the predominant mood is elevated, expansive, or irritable, accompanied by symptoms such as hyperactivity, pressured speech, racing thoughts, inflated self -esteem, decreased need for sleep, distractibility, and excessive involvement in potentially dangerous self-destructive activity.