Feudalism, also known as the feudal system, was a combination of legal, economic, military, cultural, and political customs that flourished in medieval Europe from the 9th to 15th centuries. Broadly defined, it was a way of structuring society around relationships derived from the holding of land in exchange for service or labour.

A fief was a central element in medieval contracts based on feudal law. It consisted of a form of property holding or other rights granted by an overlord to a vassal, who held it in fealty or "in fee" in return for a form of feudal allegiance, services or payments. The fees were often lands, land revenue or revenue-producing real property like a watermill, held in feudal land tenure: these are typically known as fiefs or fiefdoms. However, not only land but anything of value could be held in fee, including governmental office, rights of exploitation such as hunting, fishing or felling trees, monopolies in trade, money rents and tax farms. There never existed a standard feudal system, nor did there exist only one type of fief. Over the ages, depending on the region, there was a broad variety of customs using the same basic legal principles in many variations.