Bipolar disorder is a mood condition with distinct episodes of depression and episodes of mania or hypomania, separated by periods when mood returns to the person's usual level.
Mania is a period of raised or irritable mood with much more energy, less need for sleep, racing thoughts and risk-taking. It lasts days or weeks. Hypomania is a milder form. Bipolar I and bipolar II are the two main types.
Some of this overlaps with ADHD. Fast speech, impulsive decisions and poor sleep appear in both. The difference is the pattern over time. ADHD traits are present most of the time and have been since childhood. Bipolar episodes have a start and an end, and they're a change from how the person usually is.
The two can occur together. An assessment asks about your mood history for this reason. It also affects which medication is safe to consider.