What do we mean when we say that Mary is betrothed to Joseph?

During the time of Jesus, the Jewish marriage process involved two separate parts, the first of which was betrothal. This was an exchange of consent made between a man and a woman before witnesses. Betrothal was binding, and it could only be ended by death or divorce. After the betrothal, there was a period of several months in which the woman remained with her family. After that period was up, she would move into her husband’s home, where they lived together as husband and wife. So when the Gospels refer to Mary as being betrothed to Joseph, they are talking about the period of time after the exchange of consent but before they lived together as a married couple.