"Committee on National Security Systems Instruction (CNSSI) No. 4033 explains the nomenclature assigned to U.S., Allied, and NATO [North Atlantic Treaty Organization] communications security (COMSEC) material produced by the U.S. Government for use in National Security Systems (NSS). The information contained in this CNSSI should be made available to all U.S. Government departments and agencies, and their agents, who hold or use COMSEC material."
Committee on National Security Systems No. 4033; CNSSI No. 4033
Committee on National Security Systems: http://www.cnss.gov/