All Saints' Day is celebrated by Catholic Christians on November 1. Other Christians celebrate it as well. (May not be on the same day) It is a mandatory Catholic holiday. It is celebrated in the Catholic Church. The next day, November 2 is celebrated as All Souls' Day, souls in Purgatory are especially remembered. Both days are considered important and they are integrated with each other. The older name is All Hallows or Hallowmas
All Saints is also a Christian formula involving all the faithful saints and martyrs, known and unknown.