ATF. The Bureau of Alcohol, Tobacco, Firearms, and Explosives, Department of Justice.
27 CFR § 771.5
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 meaning provided in this subpart. Words in the plural form shall include the singular, and vice versa, and words importing the masculine gender shall include the feminine.