A manic episode is a period of abnormally elevated mood and high energy that lasts at least one week, characterized by increased activity or energy levels, impulsive behavior, and grandiose thoughts. It is a core feature of bipolar disorders, specifically in the context of Bipolar I, where the presence of at least one manic episode is required for diagnosis, while in Bipolar II, the focus is more on hypomanic episodes that are less severe but still impactful.