A "Holy Day of Obligation" is a day in the Catholic Church when the faithful are required to attend Mass. These days are significant in the church calendar and often commemorate important events in the life of Jesus Christ, the Virgin Mary, or the saints. Typically, there are several Holy Days of Obligation each year, in addition to the weekly Sunday obligation. Examples include Christmas on December 25 and the Feast of the Assumption on August 15. Failing to attend Mass on these days without a valid reason is considered a serious matter in Catholic teaching.