All Saints' Day, also known as All Hallows, Day of All the Saints, Solemnity of All Saints, or Feast of All Saints is a festival celebrated on 1 November by the Latin Church of the Roman Catholic Church and some other Western Christian traditions, and on the first Sunday after Pentecost in Eastern Catholicism and Eastern Orthodoxy, in honour of all the saints, known and unknown. The liturgical celebration begins at Vespers on the evening of 31 October and ends at the close of 1 November. It is thus the day before All Souls' Day.
Hallowmas is another term for the feast and was used by Shakespeare in this sense. However, a few recent writers have applied this term to the three days from 31 October to 2 November inclusive, as a synonym for the triduum of Hallowtide.
In Catholic theology, the day commemorates all those who have attained the beatific vision in Heaven. It is a national holiday in many historically Catholic countries. In the Catholic Church and many Anglican churches, the next day specifically commemorates the departed faithful who have not yet been purified and reached Heaven. Christians who celebrate All Saints' Day and All Souls' Day do so in the fundamental belief that there is a prayerful spiritual bond between those in heaven (the "Church triumphant"), and the living (the "Church militant"). Other Christian traditions define, remember and respond to the saints in different ways; for example, in the Bible and the Methodist Church, the word "saints" refers to all Christians and therefore, on All Saints' Day, the Church Universal, as well as the deceased members of a local congregation, are honored and remembered.
In the British Isles, it is known that churches were already celebrating All Saints on 1 November at the beginning of the 8th century to coincide or replace the Celtic festival of Samhain. James Frazer suggests that 1 November was chosen because it was the date of the Celtic festival of the dead (Samhain) – the Celts had influenced their English neighbours, and English missionaries had influenced the Germans. However, Ronald Hutton points out that, according to Óengus of Tallaght(d. ca. 824), the 7th/8th century church in Ireland celebrated All Saints on 20 April. He suggests that 1 November date was a Germanic rather than a Celtic idea.