Interstate commerce means trade, traffic, or transportation in the United States -
(1) Between a place in a State and a place outside of such State (including a place outside of the United States);
(2) Between two places in a State through another State or a place outside of the United States; or
(3) Between two places in a State as part of trade, traffic, or transportation originating or terminating outside the State or the United States.
49 CFR § 390.5
Unless specifically defined elsewhere, in this subchapter: