And the word serf comes from the Latin for service, the same word that eventually gives us words like servant. And there's some place in between a free peasant and a slave. They are bonded to the lord of the manor. In this case, it would be a duke, but you could go down this hierarchy. You could have a manor where the lord is a baron or the lord is a knight or the lord is just someone who is very wealthy and somehow got access to a fiefdom. So the serfs are bonded to the land. They can't leave without their permission.