APA Dictionary of Psychology

mood disturbance that fluctuates over a short period, most commonly between manic and depressive symptoms. In DSM–IV–TR, DSM–5, and DSM-5-TR, the term is a specifier applied to bipolar disorder characterized by four or more mood episodes over a 12-month period; the episodes must be separated by symptom-free periods of at least 2 months or must be delimited by switching to an episode of opposite polarity (e.g., a major depressive episode switches to a manic, mixed, or hypomanic episode). [coined in 1974 by U.S. psychiatrists David L. Dunner and Ronald R. Fieve]