From Wikipedia:
The banns of marriage, commonly known simply as the "banns" or "bans" /bænz/ (from a Middle English word meaning "proclamation", rooted in Frankish and from there to Old French[1]), are the public announcement in a Christian parish church or in the town council of an impending marriage between two specified persons. It is commonly associated with the Church of England and with other denominations whose traditions are similar; in 1983, the Roman Catholic Church removed the requirement for banns and left it to individual national conferences of bishops to decide whether to continue this practice.
The purpose of banns is to enable anyone to raise any canonical or civil legal impediment to the marriage, so as to prevent marriages that are invalid. Impediments vary between legal jurisdictions, but would normally include a pre-existing marriage that has been neither dissolved nor annulled, a vow of celibacy, lack of consent, or the couple's being related within the prohibited degrees of kinship.
