employment
For purposes of this chapter, the term “employment” means any service, of whatever nature, performed (A) by an employee for the person employing him, irrespective of the citizenship or residence of either, (i) within the United States, or (ii) on or in connection with an American vessel or American aircraft under a contract of service which is entered into within the United States or during the performance of which and while the employee is employed on the vessel or aircraft it touches at a port in the United States, if the employee is employed on and in connection with such vessel or aircraft when outside the United States, or (B) outside the United States by a citizen or resident of the United States as an employee for an American employer (as defined in subsection (h)), or (C) if it is service, regardless of where or by whom performed, which is designated as employment or recognized as equivalent to employment under an agreement entered into under section 233 of the Social Security Act; except that such term shall not include—