What does "bipolar" mean?

According to Dictionary.com, the word "bipolar" has four definitions. The etymology of the word "bipolar" literally means "having two poles, or extremes." This can refer to magnetism, such as the North and South Poles of the Earth.

"Bipolar" may also refer to bipolar disorder, also known as manic depressive disorder, notes Dictionary.com. This is a mood disorder in which a patient swings between mania (an elevated mood) and depression (a melancholic mood). In addition to these two definitions, "bipolar" may also refer to something characterized by two extremes or a transistor that carries both negative and positive charges. The term "bipolar" is most commonly used to refer to the mental disorder.