En banc (French: "on bench") is a legal term used to refer a case heard or to be heard before all judges of a court – in other words, before the entire bench – rather than by a panel selected from them. The equivalent terms in banc, in banco or in bank are also sometimes seen.
En banc is often used for unusually complex cases or cases considered to be of greater importance. Appellate courts in the United States sometimes grant rehearing en banc to reconsider a decision of a panel of the court (generally consisting of only three judges) where the case concerns a matter of exceptional public importance or the panel's decision appears to conflict with a prior decision of the court. In rarer instances, an appellate court will order hearing en banc as an initial matter, instead of the panel hearing it first.
Some appellate courts, such as the Supreme Court of the United States and the highest courts of most U.S. states, do not sit in panels, but hear all of their cases en banc (with the exception of cases where a judge is ill or recused).
Read more about En Banc: United States Courts of Appeals