Out of or beyond the power authority of a court or judge; beyond jurisdiction; not valid as a part of a judicial proceeding; as, extrajudicial oaths, judgments, etc., are null and void.

done outside the course of a judicial proceeding.

beyond the usual course of legal proceedings; legally unwarranted; "an extrajudicial penalty"

adj. referring to actions outside the judicial (court) system, such as an extralegal confession, which, if brought in as evidence, may be recognized by the judge during a trial.

Outside of the court system.