An oath of fealty, from the Latinfidelitas (faithfulness), is a pledge of allegiance of one person to another. Typically the oath is made upon a religious object such as a Bible or saint'srelic, thus binding the oath-taker before God.
In medieval Europe, fealty was sworn between two people, the obliged person (vassal) and a person of rank (lord). This was done as part of a formal commendation ceremony to create a feudal relationship.
Fealty and homage are a key element of feudalism. Under the feudal system, the smallest unit of land a fief could own was called a fea or fee, giving rise to the term freehold.
The term is also used by English-speakers to refer to similar oaths of allegiance in other feudal cultures, as with medieval Japan.