All Souls' Day is a time of special prayers dedicated to the dead, who in the beliefs of Catholics, can through prayers participate in Christ's victory over death. This is especially true for those who, after death, need purification in love, or purgatory, which is for many, the "vestibule of heaven."
The memory of the deceased was worshiped already back in pagan times. In ancient Rome, pagan rituals concerning death of their relatives was celebrated each February. Christians took over the tradition which did not contradict with their faith. The Christian tradition of praying for the dead dates back to 7th century.
The traditional name of the day is Dzień Zaduszny but the most popular is just Zaduszki. It corresponds with the official Church name and means a day to pray for the souls of the dead.