If your last name comes from your mother, or one of her ancestors, it's a matronymic. In most societies, matronymics are much less common than names handed down from the paternal side of the family.
Any surname that's connected to the person's mother is a matronymic. It was once fairly common for babies to be given the last name of the parent who was considered to be more important (this usually had to do with wealth or a powerful family). King Henry II of England had several surnames, one of which was the matronymic "Fitzempress," or "son of an empress." The word matronymic combines the Latin māter, "mother," and the Greek onuma, "name."