All Saints' Day is a solemn holy day of the Catholic Church celebrated annually on November 1. The day is dedicated to the saints of the Church, that is, all those who have attained heaven. It should not be confused with All Souls' Day, which is observed on November 2, and is dedicated to those who have died and not yet reached heaven.
Although millions, or even billions of people may already be saints, All Saints' Day observances tend to focus on known saints --that is those recognized in the canon of the saints by the Catholic Church.
Generally, All Saints' Day is a Catholic Holy Day of Obligation, meaning all Catholics are required to attend Mass on that day. Whenever January 1, the solemnity of Mary, the Mother of God; or August 15, the solemnity of the Assumption of the Blessed Virgin; or November 1, the solemnity of All Saints falls on a Saturday or Monday, the obligation to attend Mass is lifted. The faithful, however, are encouraged to attend Mass on those days.