Soul Saturday

Saturday of Souls (or Soul Saturday) is a day set aside for the commemoration of the dead within the liturgical year of the Eastern Orthodox and Byzantine Catholic Churches. Saturday is a traditional day for prayer for the dead, because Christ lay dead in the Tomb on Saturday. There are several Soul Saturdays throughout the year:

In the Bulgarian Orthodox Church there is a commemoration of the dead on the Saturday before the feast of Saint Michael the Archangel, i.e. on the 8th of November (instead of the Demetrius Soul Saturday). These days are devoted to prayer for departed relatives and others among the faithful who would not be commemorated specifically as saints. The Divine Services on these days have special hymns added to them to commemorate the departed. There is normally a Panikhida (Memorial Service) either after the Divine Liturgy on Saturday morning or after Vespers on Friday evening, for which Koliva (a dish made of boiled wheatberries or rice and honey) is prepared and placed on the Panikhida table. After the Service, the priest blesses the Koliva. It is then eaten as a memorial by all present.

All Orthodox and Byzantine Catholics observe Soul Saturdays on Meatfare Saturday (i.e., two Saturdays before the beginning of Great Lent); the second, third and fourth Saturdays of Great Lent; and the Saturday before Pentecost. Others, such as the Serbian Orthodox, observe commemorations of the dead on the Saturdays before August 8 and before October 24. The Russians observe memorials on the Saturdays closest to October 26 (Saint Demetrius) and September 23 (Conception of St. John the Forerunner).

Another Memorial Day, Radonitsa, does not fall on a Saturday, but on either Monday or Tuesday of the second week after Pascha (Easter). Radonitsa does not have special hymns for the dead at the Divine Services. Instead, a Panikhida will follow the Divine Liturgy, and then all will bring paschal foods to the cemeteries to greet the departed with the joy of the Resurrection.

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Wikipedia