Wiktionary
n. (context legal English) A legal document filed in connection with litigation which asks the opposing party to provide documents or other physical objects.
Wikipedia
A request for production is a legal request for documents, electronically stored information, or other tangible items. In civil procedure, during the discovery phase of litigation, a party to a lawsuit may request that another party provide any documents that it has that pertain to the subject matter of the lawsuit. For example, a party in a court case may obtain copies of e-mail messages sent by employees of the opposing party.
The responding party is required to furnish copies of any documents that are responsive to the request, except for those that are legally privileged. The responding party also can submit a response to the requestor explaining why the documents cannot be produced, for example: when the documents have been destroyed, or would be unduly burdensome to produce, or are not in possession of the party. However, the requestor then may file a Motion to Compel Discovery to still obtain the documents.
The rules governing requests for the production of documents vary from jurisdiction to jurisdiction; in the U.S. Federal court system, such requests are governed by Rule of the Federal Rules of Civil Procedure.