Odilo of Cluny in the context of Cluniac Reforms

Allhallowtide, Hallowtide, Allsaintstide, or the Hallowmas season is the Western Christian season encompassing the triduum of All Hallows' Eve (Halloween), All Hallows' Day (All Saints' Day) and All Souls' Day, as well as the International Day of Prayer for the Persecuted Church (observed on the first Sunday of November) and Remembrance Sunday (observed on the second Sunday in November) in some traditions. The period begins on 31 October annually. Allhallowtide is a "time to remember the dead, including martyrs, saints, and all faithful departed Christians." The present date of Hallowmas (All Saints' Day) and thus also of its vigil (Hallowe'en) was established for Rome perhaps by Pope Gregory III (731–741) and was made of obligation throughout the Frankish Empire by Louis the Pious in 835. Elsewhere, other dates were observed even later, with the date in Ireland being 20 April. In the early 11th century, the modern date of All Souls' Day was popularized, after Abbot Odilo established it as a day for the monks of Cluny and associated monasteries to pray for the dead.

All Souls' Day, also called The Commemoration of All the Faithful Departed, is a day of prayer and remembrance for the faithful departed, observed by Christians on 2 November. In Western Christianity, including Roman Catholicism and certain parts of Lutheranism and Anglicanism, All Souls' Day is the third day of Allhallowtide, after All Saints' Day (1 November) and All Hallows' Eve (31 October). Before the standardization of Western Christian observance on 2 November by St. Odilo of Cluny in the 10th century, many Roman Catholic congregations celebrated All Souls' Day on various dates during the Easter season as it is still observed in the Eastern Orthodox Church, the Eastern Catholic churches and the Eastern Lutheran churches. Churches of the East Syriac Rite (Assyrian Church of the East, Ancient Church of the East, Syro-Malabar Catholic Church, Chaldean Catholic Church, Syriac Catholic Church) commemorate all the faithful departed on the Friday before Lent. As with other days of the Allhallowtide season, popular practices for All Souls' Day include attending Mass offered for the souls of the faithful departed, as well as Christian families visiting graveyards in order to pray and decorate their family graves with garlands, flowers, candles and incense. Given that many Christian cemeteries are interdenominational in nature, All Souls' Day observances often have an ecumenical dimension, with believers from various Christian denominations praying together and cooperating to adorn graves.

Zaduszki (Polish: [zaˈduʂki] ) or Dzień Zaduszny (Polish: [ˈd͡ʑɛɲ zaˈduʂnɘ] ) is a Polish name for the Commemoration of All the Faithful Departed (All Souls' Day) on 2 November. The word Zaduszki originating from Dzień Zaduszny, can be roughly translated into English as "the day of prayers for the souls". On this day people visit cemeteries to light candles and pray for the souls of their faithful departed, especially those believed to be in purgatory.

The annual celebration in the liturgical year of All Souls' day was standardized and put on 2 November by St. Odilo of Cluny by the end of the 10th century. In 1311, by the decision of the Holy See, All Souls' Day was introduced into the Roman Rite and the General Roman Calendar.