[Japo]

Halloween means All Hallows Eve, All Hallows being the 1st of November. The kids' trick or treat is nowadays confined to North America --even though it was brought there from Europe maybe Germany or Netherlands I'm not sure--, but aside that the holiday is the same here. Traces back to the Celtic New Year's Eve, and the Celts left that custom pretty much all across Europe even where they were later culturally erased from, like even Spain for instance.

EDIT: The post above wasn't there before, we kind of agree.

EDIT: Here in Spain there's traditionally nothing special during the Eve, but on All Hallows itself you're supposed to pay a visit to your dead relatives at the cemetery. Which traces quite back to the Celtic belief, namely that during the night between the last day of a year and the first one of the following one --the (Celtic) New Year's Eve 31st of October--, the dead were set loose and so those gullible Celts tried to appease them and locked themselves tight at home. Later when people don't believe religiously in a holiday any longer, it tends to get from solemn to funny, adults lose interest whereas kids joyfully replace their parents in the former worship. Hence Halloween, Carnival, etc.