Feudalism

Term denoting the political and economic system that was in existence throughout the European Middle Ages.

In a stricter sense, the term refers to the legal and moral obligations between a monarch and the nobility: the granting of land in exchange for the provision of warriors. In a broader sense, the feudal system includes the bonds of loyalty all along the social ladder, especially the relationship between landowners in the country (lords of the manor) and the peasants, who were allowed to cultivate the land and enjoyed protection in return for services to the lord (work, military service).

They who grant land are usually referred to as lords; they who take it become their vassals. The structure of a feudal society implicates that a person could be both a vassal to their superior, from whom they receive land, and a lord to their inferiors, to whom they grant subdivided parts of the land.

The idea of mutual obligations and fidelity generally favours an indirect form of government; a monarch, for example, will not have direct access to his lower subjects (although he is in theory the overlord and the owner of all the land) but only to the aristocrats that are his immediate vassals.

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Further reading:
Encyclopedia Britannica Online: Feudalism