Wedding banns are notices to the parish community that two people intend to marry. They may be published in the parish bulletins at the request of the participants but are no longer required.
One may ask, what business is this to anyone except the couple and their families? The answer lies in the fact that the decision to marry is reserved not only for the couple but also for the Church, as well as the State.
For instance, the Church may refuse marriage to a couple if there is an impediment of some sort, i.e. a previous marriage that has not been annulled. The State may refuse to issue a license to marry a couple if there is too close of a relationship between a man and a woman, for example.