A vassal was a person in medieval Europe who pledged loyalty and service to a more powerful lord in exchange for protection and land. The vassal would kneel before the lord, place his hands between the lord's hands, and swear an oath of fealty, promising to fight in the lord's army, give advice, and provide other services. In return, the lord granted the vassal land called a fief and promised to protect him from enemies.

This arrangement formed the backbone of the feudal system, the way medieval society was organized for about 500 years. A powerful duke might be a vassal to a king but also have his own vassals: knights and lesser nobles who served him. This created a pyramid of loyalty, with the king at the top and layers of vassals below.

The relationship worked both ways. A vassal owed service, but the lord owed protection. If a lord failed to protect his vassal or seized his land unfairly, the vassal could rightfully break the bond.

Today, people sometimes use vassal to describe a person or country that's overly dependent on or controlled by a more powerful one, suggesting they've lost their independence.