All Souls' Day (Commemoratio omnium fidelium defunctorum), also called Defuncts' Day in Mexico, is the day set apart in the Roman Catholic Church for the commemoration of the faithful departed.
The practice of setting apart a special day for intercession for certain of the faithful departed is very old. But the first feast of general intercession was first established by Odilo, abbot of Cluny (d. 1048). The legend is given by Peter Damiani in his Life of St Odilo. According to this, a pilgrim returning from the Holy Land was cast by a storm on a desolate island. A hermit living there told him that amid the rocks was a chasm communicating with purgatory, from which perpetually rose the groans of tortured souls. The hermit also claimed he had heard the demons complaining of the efficacy of the prayers of the faithful, and especially the monks of Cluny, in rescuing their victims. Upon returning home, the pilgrim hastened to inform the abbot of Cluny, who then set the 2nd of November as a day of intercession on the part of his community for all the souls in purgatory. The decree ordaining the celebration is printed in the Bollandist Acta Sanctorum (Saec. VI, pt. i. p. 585). From Cluny the custom spread to the other houses of the Cluniac order, was soon adopted in several dioceses in France, and spread throughout the Western Church.
Just as it is the custom of French people, of all ranks and creeds, to decorate the graves of their dead on the jour des morts, so Germans stream to the graveyards once a year with offerings of flowers.
Certain popular beliefs connected with All Souls' Day are of pagan origin and immemorial antiquity. Thus the dead are believed by the peasantry of many Catholic countries to return to their former homes on All Souls' Night and partake of the food of the living. In Tyrol, cakes are left for them on the table and the room kept warm for their comfort. In Brittany, people flock to the cemeteries at nightfall to kneel bare-headed at the graves of their loved ones, and to toll the hollow of the tombstone with holy water or to pour libations of milk on it, and at bedtime the supper is left on the table for the souls. wiki