In India it is still the custom for a daughter to be offered to someone simply by word. This is called vāg-datta. This means that the father, brother or guardian of a girl has given his word that she will be married to a certain man. Consequently, that daughter cannot be married to anyone else. She is reserved by virtue of the honest words of the father or guardian. There are many instances in which the parents of a female child have given someone a verbal promise that their daughter will be married to his son. Both parties agree to wait until the boy and girl are grown up, and then the marriage takes place.
Ref >> Srila Prabhupada Vani.