A subpoena is a writ, or written command, that is issued by a legal authority. It orders an individual to appear in court as a witness. Subpoenas include specific information like time, date and the location of the courthouse. Subpoenas may also used by other legislative panels such as investigative committees.
In the absence of a subpoena, a witness is not required to attend court or provide sworn testimony in a case. A person who fails to comply with the orders on a subpoena may be punished by the law.