The Department of State has announced that certain individuals have been added to the Department of Treasury's Specially Designated Nationals and Blocked Persons List (SDN List). This decision was made under an Executive Order that reinstates certain sanctions related to Iran. As a result, any property these individuals have under U.S. jurisdiction is blocked, and Americans are generally not allowed to engage in transactions with them. More information about these sanctions can be found on the OFAC website.
Simple Explanation
The U.S. government has added some people to a list that stops them from doing business in America because of rules about Iran. This means their things in the U.S. are frozen, and Americans can't buy or sell stuff with them.