The term Halloween, and its older spelling Hallowe'en, is shortened from All-hallow-eve, as it is the evening before "All Hallows' Day"[1] (also known as "All Saints' Day").
The festival of All Saints, also sometimes known as "All Hallows," or "Hallowmas" ("hallows" meaning "saints," and "mas" meaning "Mass"), is a feast celebrated in their honour. All Saints is also a Christian formula invoking all the faithful saints and martyrs, known or unknown. In the Catholic Church, it is one of the Holy Days of Obligation
"In the Roman Catholic Church, Holy Days of Obligation or Holidays of Obligation, less commonly called Feasts of Precept, are the days on which, as (canon 1247 of the Code of Canon Law) states,
the faithful are obliged to participate in the Mass. Moreover they are to abstain from those works and affairs which hinder the worship to be rendered to God, the joy proper to the Lord’s day, or the suitable relaxation of mind and body. "
The Western Christian holiday (officially Festum omnium sanctorum in the Roman Catholic Church) falls on November 1, followed by All Souls' Day on November 2, and is a Holy Day of Obligation, with a vigil and an octave. The Eastern Orthodox Church's All Saints follows the earlier tradition kept by the whole Church of keeping the feast on the first Sunday after Pentecost and as such marks the close of the Easter season.
All Souls' Day (formally, Commemoratio omnium Fidelium Defunctorum or Commemoration of all the Faithful Departed), also called Defuncts' Day in Mexico and Belgium, is the day set apart in the Roman Catholic Church and some other churches for the commemoration of the faithful departed. The celebration is based on the doctrine that the souls of the faithful which at death have not been cleansed from venial sins, or have not atoned for past transgressions, cannot attain the beatific vision, and that they may be helped to do so by prayer and by the sacrifice of the mass.
The feast falls on November 2 and follows All Saints Day. Since the liturgical reforms of the Second Vatican Council the feast is celebrated on November 2 even in years when that date falls on a Sunday. In the traditional Latin rite, the observance is transferred to Monday, November 3 if November 2 is a Sunday, as black vestments are never permitted on Sundays.
The holiday was a day of religious festivities in various northern European Pagan traditions, until Popes Gregory III and Gregory IV moved the old Christian feast of All Saints Day to November 1. Halloween is also called Pooky Night in some parts of Ireland, presumably named after the púca, a mischievous spirit.
The Púca (Old Irish), (also Pooka, Phooka, Phouka, Púka, Pwca in Welsh, pouque in Dgèrnésiais, also Glashtyn, Gruagach) is a creature of Celtic folklore, notably in Ireland and Wales. It is one of the myriad of fairy (faery) folk, and, like many faery folk, is both respected and feared by those who believe in it.