What is a "subpoena" in legal terms?

A subpoena is indeed defined as a document issued by a court or a legal authority that demands an individual to appear in court as a witness or to produce evidence for a legal proceeding. This legal instrument plays a vital role in ensuring that parties have access to necessary evidence and witnesses, thereby promoting fairness and transparency in the judicial process.

In the context of the options presented, only the definition regarding the court order for attendance or the production of evidence accurately captures the essential function of a subpoena. The other options do not align with its purpose: a request for a legal opinion from a court relates more to motions or legal briefs; a formal notice of trial dates refers to notifications provided by the court about scheduled proceedings; and a legal agreement between parties pertains to contracts or stipulations, not the compulsory nature of a subpoena. Thus, the choice highlighting the order to attend court or produce evidence is the most precise and fitting characterization of a subpoena in legal terminology.