A more thorough explanation:

The Specially Designated Nationals and Blocked Persons List is a list maintained by the Department of Treasury’s Office of Foreign Assets Control. This list is made up of individuals and organizations that are deemed to represent restricted countries or are known to be involved in terrorism and narcotics trafficking. It is not allowed to engage in export transactions with entities that appear on this list.

For example, if a company wants to export goods to a person or organization that appears on the Specially Designated Nationals and Blocked Persons List, they are not allowed to do so. This is because the person or organization is considered a risk to national security and engaging in business with them could compromise the safety of the United States.

Another example is if a person wants to send money to someone who appears on the list. They are not allowed to do so because the person on the list is considered a threat to national security and sending them money could be used to fund illegal activities.