The form "Halloween" derives from Hallowe'en, an old contraction, still retained in Scotland , of "All Hallow's Eve," so called as it is the day before the Catholic All Saints holy day, which used to be called "All Hallows," derived from All Hallowed Souls.
In Ireland , the name was Hallow Eve and this name is still used by some older people. Halloween was formerly also sometimes called All Saints' Eve.
The holiday was a day of religious festivities in various northern European pagan traditions, until it was appropriated by Christian missionaries (along with Christmas and Easter, two other traditional northern European pagan holidays) and given a Christian reinterpretation.
Halloween is also known as the Day of the Dead, and it is a day of celebration for Wiccans and other modern pagan traditions, though the holiday has lost its religious connotations among the populace at large.
Halloween History