In Western Christianity, All Souls' Day commemorates the faithful departed. This day is principally observed in the Catholic Church, although some churches of the Anglican Communion and the Old Catholic Churches also celebrate it. The Eastern Orthodox churches observes several All Souls' Days during the year. The Roman Catholic celebration is based on the doctrine that the souls of the faithful which at death have not been cleansed from the temporal punishment due to venial sins, or have not fully been purged from attachment to mortal sins, cannot attain the beatific vision in heaven yet, and that they may be helped to do so by prayer and by the sacrifice of the Mass (see Purgatory). In other words, when they died, they had not yet attained full sanctification and moral perfection, a requirement for entrance into Heaven. This sanctification is carried out posthumously in Purgatory.
All Souls' Day is also known as the Feast of All Souls, Commemoration of all the Faithful Departed. The official Latin designation Commemoratio omnium Fidelium Defunctorum, on which this last name is based, is rendered more literally in Portuguese Comemoração de todos os Fiéis Defuntos and many other languages. Day of the Dead (Día de los Muertos or de los Difuntos) is used in Spanish-speaking countries, and Thursday of the Dead (Yom el Maouta) in Lebanon, Israel and Syria.http://en.wikipedia.org/wiki/All_Souls'_Day