What is Halloween?

Halloween traces its roots to a pagan festival of ancient Ireland known as Samhain.  
Samhain is considered the time when the 'door' to the other world opens and dead communicates with the earthly beings. It also traces routes from All Hallow's Eve and All Saint's Day celebrated in many parts of the world.

Thus, to scare the dead away from their homes, the Irish people started placing lanterns carved of turnips outside their home. 

However, when the Irish migrated to North America, the land of Pumpkins, they couldn't find many turnips and started crafting the Pumpkins, which were much ideally suited for the purpose. 

What is Halloween?