Dictionary.net

A public announcement of an intended marriage, required by the English law to be made In a church or chapel, during service, on three consecutive Sundays before the marriage is celebrated. The object is to afford an opportunity for any person to interpose an objection if he knows of any impediment or other just cause why the marriage should not take place. The publication of the bans may be dispensed with by procuring a special license to marry.

The giving public notice or making proclamation of a matrimonial contract, and the intended celebration of the marriage of the parties in pursuance of such contract, to the end that persons objecting to the same, may have an opportunity to declare such objections before the marriage is solemnized. Poth. Du Mariage, partie 2, c. 2. Vide Ban.