writ issued by a government agency, most often a court, to compel testimony by a witness or production of evidence under a penalty for failure

A subpoena /səˈpnə/ is a written order that requires a witness to give testimony, or their statement of truth. A subpoena is usually issued by a court. If a person or organization does not respond to the subpoena, they may be punished by the court.

There are two types of subpoena. Subpoena ad testificandum means a person must give testimony directly to the court. This can be in person or by telephone. Subpoena duces tecum means physical evidence must be brought to the court. This type of subpoena is usually used for documents. Sometimes the documents can be mailed to the court.