A U.S. person for tax purpose includes any of the following: (see the IRS website):
A U.S. Citizen, which is anyone with a U.S. passport,
A green card holder (see: http://www.irs.gov/Individuals/International-Taxpayers/Alien-Residency—Green-Card-Test), or
A U.S. resident for tax purposes – most commonly defined as someone who spends more than 183 days in the US under the Substantial Presence Test. A U.S. resident for tax purposes is commonly referred to as a resident alien.