The U.S. State Department, under the authority of Executive Order 13224, has designated Abdul Malik al-Houthi, Abd al-Khaliq Badr al-Din al-Houthi, and Abdullah Yahya al Hakim as Specially Designated Global Terrorists. This means they are recognized as leaders of Ansarallah, a group whose assets and property are blocked. The order prohibits prior notification since it could make the measures ineffective, especially for those in the U.S. who might quickly transfer funds. This official designation by Secretary of State Michael R. Pompeo was published in the Federal Register.
Simple Explanation
The U.S. government said that three people who lead a group called Ansarallah are officially called "bad guys" in a special way because they do things like being a part of bad plans, and this means that their money and stuff in the U.S. are frozen.