Hallowe'ens Past ~ The Eve of All Saints' Day
October 31

"Trick-or-treat" ~ n., v., & interj. esp. N. Amer.  a Halloween custom in which children, dressed in costumes, knock on the doors of neighbours soliciting a treat of esp. candy, threatening, in accordance with tradition, to commit a prank if denied.  " trick or treat!" ~ interj. Shouted by children while trick-or-treating.

"Halloween apples" ~ interj. Cdn (Prairies) uttered by children going door to door on Halloween to collect candies etc.

~ The Canadian Oxford Dictionary, Edited by Katherine Barber, Oxford University Press, 1998.