Age.

Age. The period during which, after distillation and before bottling, distilled spirits have been stored in oak containers. Age for bourbon whisky, rye whisky, wheat whisky, malt whisky, or rye malt whisky, and straight whiskies other than straight corn whisky, means the period the whisky has been stored in charred new oak containers.

Source

27 CFR § 5.11

Scoping language

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 ascribed in this section. Any other term defined in the Federal Alcohol Administration Act and used in this part shall have the same meaning assigned to it by such Act.