Relinquishment of United States nationality
Under United States federal law, a U.S. citizen or national may voluntarily and intentionally give up that status and become an alien with respect to the United States. Relinquishment is distinct from denaturalization, which in U.S. law refers solely to cancellation of illegally procured naturalization.
Source: Wikipedia — Relinquishment of United States nationality (CC BY-SA 4.0)