Final answer:
In medieval Europe, a fief was the land granted to a vassal or knight as part of the feudal system, entailing service and protection in exchange.
Step-by-step explanation:
Land granted to a vassal or knight during the medieval period in Europe was known as a fief. This system, part of the larger feudal system, was based on reciprocal relationships involving protection, service, and land grants. A lord would provide a fief to his vassal, who, in return, would owe military service and other duties to the lord. These fiefs were the cornerstone of feudal society, providing economic sustenance and social status to the vassals and knights, while also ensuring a lord's lands were protected and productive.