All Hallows' EVE, commonly known as Halloween, is an annual holiday celebrated on October 31st. It is believed to have originated from the ancient Celtic festival of Samhain, which was a celebration of the end of the harvest season and the beginning of winter. The term All Hallows' EVE can be abbreviated to 'Halloween' or 'All Hallow's EVE', and the crossword solution for this term is 'EVE' (3 letters).