Paroikoi
Paroikoi is the term that replaced "metic" in the Hellenistic and Roman period to designate foreign residents.
In the Byzantine Empire, paroikoi were non-proprietary peasants, hereditary holders of their land, irremovable as long as they paid their rent. They appeared in the Justinian code, which prohibited this status; so it remained provisionally clandestine.
Paroikoi are comparable to the western concept of serfs and appear to be widespread by the 13th century.