A more thorough explanation:

Villein socage is a type of land tenure where a tenant holds lands in exchange for providing the lord with husbandry-related service instead of military service. It is a type of socage, which is a type of lay tenure.

For example, if a peasant had to help the lord with sowing or reaping at specified times, the tenure was usually called socage. This was originally the tenure of socmen, but it became a generic term for all free services other than knight-service, serjeanty, or spiritual service.

Free socage is socage in which the services were both certain and honorable. By the statute 12 Car. 2, ch. 24 (1660), all the tenures by knight-service were, with minor exceptions, converted into free socage.

Villein socage, on the other hand, is socage in which the services, though certain, were of a baser nature than those provided under free socage.