IRS definition of U.S. person: What you should know

The term ''United States person'' means: a citizen or resident of the United States, a domestic partnership, a domestic corporation, any estate other than a foreign estate, or any other person that is not a foreign person.

This also includes a trust if a court within the United States is able to exercise primary supervision over the administration of the trust, and one or more United States persons have the authority to control all substantial decisions of the trust.

This is defined by the IRS. More information can be found here.