n. in law, the legal means by which a person is required to appear in court or a defendant is given notice of a legal action against him/her/it. When a complaint in a lawsuit is filed, it must be served on each defendant, together with a summons issued by the clerk of the court stating the amount of time (say, 30 days) in which the defendant has to file an answer or other legal pleading with the clerk of the court, and sent to the plaintiff. New York has an unusual system in which a summons may be served without a complaint. A subpena is similar to a summons but is a notice to a witness to appear at a deposition (testimony taken outside court), or at a trial. A subpena duces tecum is an order to deliver documents or other evidence either into court or to the attorney for a party to a lawsuit or criminal prosecution. An order to show cause is a court order to appear in court and give a reason why the court should not issue an order (such as paying temporary child support). The summons, complaint, subpena, subpena duces tecum and order to show cause must all be "served" on the defendant or person required to appear or produce, and this is called "service of process." Service of process is usually made by an officer of the court such as a deputy sheriff or marshal, or a professional process server, but can be performed by others in most jurisdictions.