Final answer:
The system of mutual obligations between the serfs and the lords in medieval Europe, including tenure on the land by the serfs, was known as the feudal system.
Step-by-step explanation:
The reciprocal obligations of serfs and lords and the serf's continuing tenure on the land were known as the feudal system. This system included a mutual exchange where the lord offered protection and land, in return for the serf's labor and service. The manorialism aspect of this system means that serfs worked the land on a manor, which was closely administrated by the lord. They owed their lord service, a share of their produce, and had very limited rights; serfs were essentially bound to the land they worked but were not property that could be bought or sold. The feudal system was the economic and political foundation of medieval Europe, and, although serfdom was abolished in Russia in the 19th century, it had for centuries shaped the social structure and hierarchy of society.