Also known as All Hallows Day, it is commonly celebrated on Nov 1st. This is a time set aside to remember and honor all the good saints that have come before us.
In the beginning, martyrs were honored on the day of their individual death. Eventually, churches started consolidating them into a single day in order to remember them all at once. Which is where the All Saints Day originated from. This started in Rome around the 7th Century after Pope Boniface IV dedicated the Pantheon.
All Saints Day has many different meanings for different churches. Click here if you would like to learn more about this holiday.