A non-disclosure agreement is a contract signed by one or more parties which prevents them from disclosing specified information under penalty of prosecution within the terms of the Espionage Act. Anyone who is to be given access to classified government materials, such as the Stargate Program, must first sign such a document. (SG1: "Secrets", "Moebius, Part 1") (SGU: "Air, Part 1")
Though the documents are usually fairly small, Malcolm Tunney had a considerably longer, more detailed version printed and issued to the scientists attending his conference. (SGA: "Brain Storm")