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, as originally laid out in the Bottled-in-Bond Act of 1897.
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).
One purpose of the Bottled-in-Bond Act was to create a standard of quality for Bourbon whiskey. Prior to the Act’s passage, much of the whiskey sold as straight whiskey was anything but. So much of product was adulterated – flavored and colored with iodine, tobacco, and other substances – that some perceived a need for verifiable quality assurance. The practice was also connected to tax law, which provided the primary incentive for distilleries to participate. Distilleries were allowed to delay payment of the excise tax on the stored whiskey until the aging of the whiskey was completed.
Source: Bottled in bond – Wikipedia