A subpoena refers to an order issued by a court that requires an individual to appear in person at a certain place (usually a court) at a particular date and time in order to testify as a witness for a case. A person who does not adhere to a subpoena can be punished by the court.
Justipedia explains Subpoena
There are two common types of subpoenas. The first is a subpoena ad testificandum. This subpoena requires a person to orally testify before a court either by phone or in person. The second subpoena is a subpoena duces tecum. It requires a person or organization to provide physical evidence before the court. This type of subpoena is typically used for obtaining documents that are important to the case as a whole or to a specific issue of the case.