Halloween (or Hallowe'en), October 31:
The word derives from "All Hallows' Eve", which denotes the evening before All Hallows' Day (All Saints' Day), a Christian feast day.
All Saints' Day, November 1:
Also known as the Feast of All Saints. It's the day we Catholics honor all the saints in Heaven, not only the canonized, recognized saints who have their own particular feast days on the Church calendar. There are many millions of saints in Heaven who are not canonized, most of whom are obviously unknown to us, and this is the day we celebrate those myriad holy men and women.
All Saints' Day is a holy day of obligation, and so to willfully miss mass on this day is a grave sin for Catholics. (In other words, get to mass!)
All Souls' Day, November 2:
This is the day we remember and pray for all the souls in Purgatory. These souls are not forgotten by the universal Church, and they benefit from the prayers of the faithful as they steadily approach perfection and the Beatific Vision. Often, Catholic parishes invite parishioners to write the names of their deceased loved ones in a "Book of Remembrance", to have prayers and masses offered for these souls during the month of November.
All Souls' Day is not a holy day of obligation.
And, I guess this very little teaching qualifies as a Little Teaching, so it gets the icon!