The Department of State has identified individuals who have been added to the Treasury Department's Specially Designated Nationals and Blocked Persons List, due to their involvement in harmful activities linked to the Russian government. As a result, the property and interests of these individuals in the U.S. are blocked, and U.S. citizens are generally banned from conducting transactions with them. The full list can be accessed through the Office of Foreign Asset Control's website.
Simple Explanation
The U.S. Government has decided to stop some people from doing business in the U.S. because they did something harmful with the Russian government. This means these people can't use their money or things in the U.S., and Americans aren't allowed to trade with them.