functus officio, Latin for “having performed his office,” is a legal term used to indicate that a public official, court, governing body, or statute retains no legal authority because his or its duties and functions have been completed. The term is most commonly used by a higher court as a justification for vacating or overruling all or part of a lower court’s opinion. For example, if a United States federal court decides that a law comports with the requirements of due process, the court cannot then attempt to strike the law simply because the law is unwise because the court’s due process determination renders it functus officio in the particular case.