What is the difference between manic depression, bipolar and split personality?

Terms: Manic depression is an older term for bipolar disorder -- a condition with episodes of both depression and mania or hypomania. In hypomania, the person has greatly increased energy, less need for sleep, racing thoughts, etc. Mania has all this plus often psychosis with hallucinations & delusions. "split personality" is a non-medical term describing someone who behaves unpredictably.

All in a name: Manic depression is the historical name for now termed bipolar affective disorder witch is a disorder of mood split personality aka multiple personality disorder and now referred to as dissociative identity disorder is a condition inflicting an individual to manifest distinct personalities. Each with characteristic patterns of thinking feeling and relating to others and the world.

Bipolar: Bipolar/manic depression are interchangeable terms, with bipolar disorder being the more modern, clinical term. Bipolar disorder refers to extreme swings of mood from depression to mania and back again. The term "split personality" does not exist as an official diagnosis. Effectively the term is meaningless.