The country with a flag featuring a single red star is Vietnam. The flag consists of a bright red field with a large yellow star at its center. The red color symbolizes the blood and sacrifices made by the Vietnamese people in their struggle for independence and unity, while the yellow star represents the unity of the workers, peasants, soldiers, and intellectuals in building socialism. The flag was adopted officially on November 30, 1955, and it reflects Vietnam's history and cultural identity.