The Fundamentals of manors and a knight's fee:
On the one hand, the king granted an individual the use of certain lands, often called a manor. This was one side of the arrangement. On the other hand, in return for the grant, the king took back the obligation of the fortunate grantee to provide recompense or 'service' to the king - the most common form in medieval times was called 'knight service'. Hence, the individual held the lands by service of one knight's fee.