This indicates that entry to the US is not guaranteed by a visa: Issuance of a visa does not guarantee entry to the United States. A visa simply indicates that

This indicates that entry to the US is not guaranteed by a visa: Issuance of a visa does not guarantee entry to the United States. A visa simply indicates that a U.S. consular officer at an American embassy or consulate has reviewed the application and that officer has determined that the individual is eligible to enter the country for a specific purpose. The CBP Officer at the port-of-entry will conduct an inspection to determine if the individual is eligible for admission under U.S. immigration law. https://www.cbp.gov/travel/international-visitors/visa-waiver-program/requirements-immigrant-and-nonimmigrant-visas https://www.cbp.gov/travel/international-visitors/visa-waive...