If a decision was made en banc by an appeals court, a human rights tribunal, or some other legal body, it means that all or most of the judges of that court were present.
Sometimes an appeals court or other tribunal is able to make a decision with only a small group of its judges. In that case, if the defendant or plaintiff disagrees with the outcome, they might ask for an "en banc rehearing," with more judges present to listen to the case again. In the U.S., the Supreme Court is the final court of appeal, so it usually makes its decisions en banc. The term en banc is borrowed from French, which used to be the most prominent language of the law in Europe and beyond.