A command, issued under a court's authority, to a witness to appear and give testimony.
Source: U.S. Courts
A process issued by a court compelling a witness to appear at a judicial proceeding. Sometimes the process will also direct the witness to bring documentary evidence to the court.
Source: Office of Child Support Enforcement.
An official order to go to court at a stated time. Subpoenas are commonly used to tell witnesses to come to court to testify in a trial.
Source: California Courts.