Mood is a person's emotional state for an undefined period of time. There are several classes of mood disorders: bipolar I, bipolar II, dysthymia, and cyclothymia. Bipolar I disorders include one or more manic episodes with or without depression. Bipolar II disorders have one or more major depressive episodes in the presence of hypomania, but no mania. Dysthymic disorders are characterized by at least two years of minor depression, while cyclothymic disorders include both hypomania and minor depression.