Bipolar disorder is the new name for what used to be called manic depression.
It better describes the exaggerated swings of mood from one extreme to another characteristic of this illness. Some only experience attacks of mania, without the subsequent steep slide into depression. Episodes can range from mild to severe. The less severe form of elevated mood, or 'high', is called 'hypomania'. Mania' is the word used to describe the most severe form of the disorder.