Princess (プリンセス) is a class that certain female royalty belong to. In Fire Emblem Gaiden, it is the promotion of the priestess class, exclusive to Celica. The Gaiden, Princesses can use swords and Black Magic.
In Fire Emblem: Genealogy of the Holy War it is a class exclusive to Raquesis, which generally serves best as support-based unit, at least until promotion into the formidable Master Knight class. The Genealogy of the Holy War Princess acts as the female counterpart to the male Prince class.