subpoena, formal instrument issued by a court, grand jury, legislative body or committee, or duly authorized administrative agency commanding an individual to appear before it at a specific time to give testimony, oral or written, in the matter identified in the document. The subpoena is used only in common-law countries, but it is similar to the citation or vocatio in jus of civil law or canon law. A subpoena duces tecum commands the recipient to produce certain evidence, usually documents or papers, that is demanded.