Serfs were agricultural laborers in the Middle Ages who were bound to work on a specific piece of land owned by a lord. They were not slaves, as they could not be bought or sold, but they had limited rights and were required to provide labor, produce, or services in exchange for protection and the right to live on the land. Serfdom was a key part of the feudal system, which structured society around relationships derived from the holding of land. Over time, the decline of serfdom occurred due to economic changes and the rise of towns and trade, leading to greater freedom for many serfs.