How is manic depression different from bipolar disorder?

Same thing: Manic depression is the old term 4 the same illness.

NOT REALLY: The terms are interchangable. Bipolar I and bipolar II, In the first, manic phases are more severe, and in the second, depressive phases are more severe. There is also cyclothymia which is a low grade version of bipolar disorder in general, where mood swings are not as severe in either direction, manic or depressive. No one knows how it develops, other than a mystery of genetic confluence.