Definition:
"Specially designated nationals" are organizations and individuals who are restricted from doing business with the United States or American companies, or Americans.. This includes terrorist organizations, individual terrorists, and state sponsors of terrorism (such as Iran, and North Korea). The list of "specially designated nationals" is maintained by the U.S. Department of the Treasury's Office of Foreign Assets Control (OFAC).
More Information: The SDN List | Iran, State Sponsor | North Korea