All Souls Day
In a similar spirit to All Saints Day, the celebration of the previous day, this Catholic mass-celebration commemorates the souls of all the departed in one go, in this case with the hope that the devotions of the living will enable them to escape the chains that bind them to the Earth and their past sins.
The doctrinal basis of the observation is that departed souls who are for some reason imperfect, ie, not perfectly cleansed of sins, are barred from entry into the celestial afterworld. The living can assist these disembodied penitents on their journey through the Pearly Gates through prayer and sacrifice, as well as with special Masses, read on this particular day.

The feast of this day is closely linked to the one preceding, the Day of All Saints, and represents a shift in perspective, as the living turn their attention away from those already in Heaven, the saints, to those in Purgatory, the sinners.
This celebration also coincides with the second of the Mexican days of the dead, the Day of the Dead proper, when the memory and spirits of the adult dead is venerated.
In the early Church a record was kept of the departed of the community, and their names were read out and remembered every year on certain days (eg. Whitsuntide). As the Church grew in scope, the demands of mass spirituality created the need for a collective day of commemoration, without remembrance of particular names.
This solemnity is always celebrated on 2 November, unless that day coincides with a Sunday or another Christian holy day, in which case it is celebrated on the 3rd.