A prioress is a nun, generally in charge of an abbey. They were very pious (as you can tell by how the prioress starts out her tale with a prayer). Her tale is really preachy. Her reverence for chastity and her harsh judgment of the Jews are both reflections of common medieval Catholic beliefs. The violent nature of the events in the story seem to be in contradiction to a personality as sensitive as the Prioress's is supposed to be, suggesting that she may be much tougher than she wishes to reveal.