What is the meaning of Bottled_in_bond?

Of a distilled beverage: aged and bottled according to a set of legal regulations contained in the U.S. government's Standards of Identity for Distilled Spirits, as originally specified in the Bottled-in-Bond Act of 1897. Such beverages must be the product of one distillation season (January–June or July–December) by one distiller at one distillery, and 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).

Source: wiktionary.org