Importation. The bringing of a firearm within the limits of the United States or any territory under its control or jurisdiction, from a place outside thereof (whether such place be a foreign country or territory subject to the jurisdiction of the United States), with intent to unlade. Except that, bringing a firearm from a foreign country or a territory subject to the jurisdiction of the United States into a foreign trade zone for storage pending shipment to a foreign country or subsequent importation into this country, under Title 26 of the United States Code, and this part, shall not be deemed importation.
27 CFR § 479.11
When used in this part and in forms prescribed under this part, where not otherwise distinctly expressed or manifestly incompatible with the intent thereof, terms shall have the meanings ascribed in this section. Words in the plural form shall include the singular, and vice versa, and words importing the masculine gender shall include the feminine. The terms includes and including do not exclude other things not enumerated which are in the same general class or are otherwise within the scope thereof.