The Samhain Festival.

Okay, maybe a bit late, but since it's not Easter yet, it can't be “figs after Easter” either.
Where does the name Halloween come from?
This is the night before All Saints' Day, a Christian holiday celebrated on November 1. The festival originated in Celtic culture and was known as Samhain, which means “end of summer”.

During Samhain, the Celts believed that the line between the world of the living and the dead was temporarily blurred, allowing the ghosts of deceased relatives and ancestors to return to the world of the living.
People wore costumes and masks to disguise themselves and protect themselves from any evil ghosts that could also appear.
As Christianity spread, the festival of Samhain was blended with the Christian tradition of All Saints' Day and All Souls Day, and eventually the name “All Hallows' Eve” was used to denote the night before All Saints' Day. Over time, the name was changed to “Halloween” as we know it today.