All Souls Day is a solemn feast in the Catholic church commemorating all of those who have died and now are in Purgatory, being cleansed of their venial sins and the temporal punishments for the mortal sins that they had confessed and atoning before entering fully into Heaven.
There is a special plenary indulgence that can be gained for the souls in Purgatory on All Souls Day. A plenary indulgence removes all temporal punishment for sin--and so, in effect, releases a soul from Purgatory. To gain this indulgence, one must visit a church, recite one Our Father and the Creed, receive Communion, and pray one additional Our Father and one Hail Mary for the intentions of the Holy Father. The final requirement is to take part in the Sacrament of Confession, which can be done up to seven days before or afterwards. Since most Catholic parishes offer Confession on Saturday, one can go to Confession on a Saturday, and then fulfill the rest of the requirements on All Souls Day itself.