Whiskey made, distilled, and bottled at same distillery at least 4 years old.

More specifically

Bottled in bond is a label for an American-made distilled beverage that has been aged and bottled according to a set of legal regulations contained in the United States government’s Standards of Identity for Distilled Spirits,^[1] as originally laid out in the Bottled-in-Bond Act of 1897. As a reaction to widespread adulteration in American whiskey, the act made the federal government the guarantor of a spirit’s authenticity, gave producers a tax incentive for participating, and helped ensure proper accounting and the eventual collection of the tax that was due. Although the regulations apply to all spirits, most bonded spirits are whiskeys in practice.

To be labeled as bottled-in-bond or bonded, the liquor must be the product of one distillation season (January–June or July–December) by one distiller at one distillery. It must have been aged in a federally bonded warehouse under U.S. government supervision for at least four years and bottled at 100 (U.S.) proof (50% alcohol by volume). The bottled product’s label must identify the distillery where it was distilled and, if different, where it was bottled.^[2][3] Only spirits produced in the United States may be designated as bonded.

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