Commonly:
* US Dollar: Referring to the currency of the United States.
* United States: The full name of the country.
Less common but still possible:
* US Navy: A branch of the United States Armed Forces.
* US Army: Another branch of the United States Armed Forces.
* US Mail: The postal service of the United States.
* US Airways: A former airline (now merged with American Airlines).
* US Open: A major tennis tournament held in the United States.
It would be helpful to know the context of the abbreviation to provide the most accurate answer. Please provide more information, such as the sentence or topic the abbreviation appears in.