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. This solemnity is a Holy Day of Obligation which means participation in the special Mass or Vigil Mass for the Solemnity is as important as our regular Sunday obligation. In the United States, the obligation of participating in the Eucharist is waived when the Solemnity is on a Monday or Saturday. We still, however, celebrate the Solemnity.