The agreement between a lord and his vassal was that the lord was responsible for providing the vassal with a piece of land as well as protecting the vassal, while the vassal was responsible for pledging his allegiance to the lord when it came to political, military and financial needs. This agreement was a part of feudalism, which was the governmental structure during the medieval period.
This feudal system was a system that aimed to please both parties. When both parties agreed, the vassal would make a handsome sum and the lord would secure his influence. The two would pledge themselves during a public ceremony and the agreement, which the ceremony created, was then known as a fief.