A vassal or feudatory is a person who has entered into a mutual obligation to a lord or monarch in the context of the feudal system in medieval Europe. The obligations often included military support and mutual protection, in exchange for certain privileges, usually including the grant of land held as a fiefdom. The term can be applied to similar arrangements in other feudal societies. In contrast, a fidelity, or fidelitas, was a sworn loyalty, subject to the king.
Read more about Vassal: Western Vassalage, Difference Between "vassal" and "vassal State"