To disbar is to officially take away a lawyer’s license to practice law. If a practicing lawyer gets caught doing something illegal or crazy, it’s time to disbar.
“The bar” is the exam that lawyers-to-be must pass after law school so they can practice law. The word bar comes from the wooden bar that surrounds the judge, where the barrister (lawyer) states a case. If you're disbarred, you can no longer practice. A lawyer found guilty of a crime or any other unethical behavior could be disbarred. Getting disbarred is a serious matter — you can tell because it happens to lawyers on TV shows all the time.