ATF officer. An officer or employee of the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) authorized to perform any function relating to the administration or enforcement of this part.
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.