The official name of the celebration in the Roman Rite liturgy of the Roman Catholic Church is "The Commemoration of All the Faithful Departed". Another popular name in English is Feast of All Souls. In some other languages the celebration, not necessarily on the same date, is known as Day of the Dead.
The Western celebration of All Souls' Day is on 2 November and follows All Saints' Day. In the ordinary form of the Roman Rite, if 2 November falls on a Sunday, the Mass is of All Souls, but the Liturgy of the Hours
is that of the Sunday, though Lauds and Vespers for the Dead in which
the people participate may be said. In the extraordinary form of the
Roman Rite and in the Anglican Communion, All Souls Day is instead
transferred, whenever 2 November falls on a Sunday, to the next day, 3
The Eastern Orthodox Church dedicates several days throughout the
year to the dead, mostly on Saturdays, because of Jesus' resting in the Holy Sepulchre on that day. In the Methodist Church, saints refer to all Christians and therefore, on All Saint's Day, the Church Universal, as well as the deceased members of a local congregation are honoured and remembered.
Byzantine Emperor, Leo VI "the Wise" (886–911). His wife, Empress Theophano—commemorated on 16 December—lived a devout life. After her death in 893,
her husband built a church, intending to dedicate it to her. When he
was forbidden to do so, he decided to dedicate it to "All Saints", so
that if his wife were in fact one of the righteous, she would also be
honored whenever the feast was celebrated.
According to tradition, it was Leo who expanded the feast from a
commemoration of All Martyrs to a general commemoration of All Saints,
whether martyrs or not.