G-4 Visa = The G-4 diplomatic Visa is a nonimmigrant Visa issued to officers or employees of international organizations of any rank to enter into the U.S. to engage in their respective activities. The staff and immediate family members (spouse and children) of the principal G-4 Visa holders also qualify for G-4 Visas.

US Person = a person born in the United States or naturalized as a US citizen. You can also be a US citizen, even if born outside of the United States if one or both of your parents are US citizens. Non-US citizens can also be US persons. For example, 'tax residents' of the United States are also considered US persons, as are Green Card holders.

For a complete definition, please refer to the Classification of Taxpayers for U.S. Tax purposes : https://www.irs.gov/individuals/international-taxpayers/classification-of-taxpayers-for-us-tax-purposes