Question

who is called vassal

Answer 1

vassal[1] is a person regarded as having a mutual obligation to a lord or monarch, in the context of the feudal system in medievalEurope. The obligations often included military support and mutual protection, in exchange for certain privileges, usually including land held as a tenant or fief.[2] The term is applied to similar arrangements in other feudal societies.

Answer 2

vassals-small states under the rule of an Empire