Canadians recognize two spellings for the secular holiday celebrated on October 31. Hallowe'en was the traditional form once taught in schools, but a simplified spelling, Halloween, has become more common.
In Western Christianity, November 1 has been celebrated since the 8th century as the festival of All Hallows Day, now better known as All Saints Day. (Hallow is an old English word for a holy person or saint.)
Just as the day before Christmas is called Christmas Eve, so October 31, the day before All Hallows Day, came to be known by the early 1700s as All Hallow Even (that is, "All Saints Eve"). Eventually, the name was contracted to Hallowe'en or simply Halloween.