Liter.
Liter. A metric unit of capacity equal to 1,000 cubic centimeters or 1,000 milliliters of alcoholic beverage, and equivalent to 33.814 fluid ounces.
Source
27 CFR § 19.1
Scoping language
As used in this part, the following terms shall have the meanings indicated unless either the context in which they are used requires a different meaning, or a different definition is prescribed for a particular subpart, section, or portion of this part: