A more thorough explanation:

Definition: Grass hearth was a customary service that a tenant had to perform for their lord. It involved the tenant bringing their plow to the lord's land and plowing it for one day.

Example: In medieval England, a tenant who held land from a lord was required to perform various services in return for the use of the land. One of these services was the grass hearth, which involved plowing the lord's land for a day. This was usually done in the spring, before the planting season began.

Explanation: The grass hearth was a way for lords to ensure that their land was properly prepared for planting. By requiring their tenants to perform this service, lords could ensure that their land was plowed and ready for planting when the time came. The grass hearth was also a way for lords to maintain control over their tenants, as failure to perform this service could result in the loss of their land.