I mean, what a holiday! Masquerade parties! Candy! Ghosts! Draculas! Werewolf Barmitzvah! Mummies! Witches! Creatures From Black Lagoons! The Skeleton Dance! Horrible Monsters Defying Description! Zombies Intent On The Destruction Of Society Itself! Whatever THIS is!
So: All Hallow's Eve. Also called Samhain. The night before the Day Of The Dead. The Celtic New Year.
The good ones always collect lots of names. Here's the point, though: In many (most?) traditional cultures, there weren't four seasons, but only two. And this is the night that we pass from one (Summer, if you like) into the other. It is the transition, the cusp into the dead time of year, and so this is the night on which it is supposed that the veil between the world of the living and the world of the dead is at its thinnest, its most porous.
So definitely girls should wear their sluttiest costumes and we should all watch Peter Jackson's wonderful wonderful WONDERFUL gorefest Brain Dead/Dead Alive.
Whatever. Have a big bonfire and remember your forebears or go out and stuff your gob with twix. I don't care; just so it matters. Halloween has everything that a holiday should have and the wheel of the year is better for it.