The serfs and villeins, who were unfree, but not slaves, were usually at the lowest level. In some places there were times when there were slaves also, and they would have been lower than serfs....
Serfs were slaves and they owed everthing to the Lord (landlord).
Serfs were not slaves. Some of them really had no need for money, because they paid rent in labor or a part of the crop, and...