All Saints Day is a Christian holiday that takes place on 1st November every year. The day was intended to recognize and honor all of the saints in the Christian church, a large number of whom were martyrs. The day was set aside by the church for the purpose of celebrating more than 10,000 recognized saints. All Saints Day was historically referred to as Hallomas.
Both All Souls Day and All Saints Day were, in fact, originally in May. The days were moved to 1st and 2nd November respectively in a bid to try and downplay the Pagan holidays of All Hallows Eve (Halloween) and Dia De Loss Muertos. This was because religious leaders believed that these pagan holidays were far too popular to actually try and ban them outright but believed that by moving the Christian holidays to these times, the pagan holidays might begin to slowly but surely die off.
Many historically Catholic nations actually have All Saints Day as a national holiday. In both the Catholic church and a number of Anglican churches, the next day specifically honors those departed faithful who have nonetheless not yet been given purification and attended to Heaven.
Those Christians who celebrate All Saints Day as well as All Souls Day believe that there is a prayerful bond between the living (known as the Church Militant), those who are in Heaven (the Church Triumphant) and those who are in purgatory (known as the Church Suffering).