Liter. A metric unit of capacity equal to 1,000 cubic centimeters at 20 degrees C. or 33.814 United States fluid ounces at 68 degrees F. of alcoholic beverage.
27 CFR § 24.10
When used in this part and in the forms prescribed under this part, terms will have the meanings ascribed in this section. Words in the plural form also include the singular, and vice versa, and words indicating the masculine gender also include the feminine. The terms includes and including do not exclude items not enumerated which are in the same general class. The definitions in this section do not supersede or affect the requirements of part 4 of this chapter, relative to the labeling of wine under the provisions of the Federal Alcohol Administration Act (49 Stat. 981; 27 U.S.C. 205).