In plain words
What bipolar disorder is
Bipolar disorder is a long-term mood condition. People with it have periods of very low mood (depression) and periods of unusually high or irritable mood, called mania or, in a milder form, hypomania, and these changes can disrupt work, relationships and everyday life.
It is diagnosed by a doctor after ruling out physical causes and looking carefully at the pattern of mood over time. Treatment usually combines medication, psychological therapy and steady day-to-day routines, with regular review.
This is general information, not a diagnosis. Source: Healthdirect: Bipolar disorder.