Under the FATCA regulations, the term US person is defined as:
a citizen or resident of the United States;
a partnership or corporation created or organised in the United States;
an estate (other than a non U.S. estate);
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;
the United States Government (including an agency or instrumentality thereof);
a US State (including an agency or instrumentality thereof);
the District of Columbia (including an agency or instrumentality thereof)