It is also Brexit day, the day the UK leaves the EU.
It is held the day before All Saints'Day, which is a Christian festival used to celebrate recognised saints.
The word Halloween comes from Hallowe'en, meaning "hallowed evening" or holy evening.
The word itself is a Scottish term for All Hallows Eve - the evening before All Saints' Day.
It is widely thought that Halloween traditions came from Celtic harvest festivals of Samhain, although some people support the view that Halloween began independently as a Christian festival.
Samhain was a celebration of the end of the harvest season, and means "summer's end."
HALLOWEEN is the best time year - pumpkins, sweets, spookiness and scary costumes... what more could you ask for?
Halloween activities typically involve trick or treating, dressing up in fancy dress and carving pumpkins.
People at this time thought the walls between worlds were thin and ghosts could pass through into our realm, and it was feared they may damage crops for the next season.
To appease any spirits, Gaels would set up places at their dinner tables for the spirits and light bonfires to scare off evil spirits.
There are a number of ways to celebrate the festival, whether you want to go out or enjoy it from the comfort of your home.
Halloween — it's not just for the kids. Though we all eventually outgrow our trick-or-treating days, that doesn't mean we have to put the holiday behind us entirely. In fact, there may be even more to do on Oct. 31 as an adult. Here are just a few of our favorite options.
Dressing up in fancy dress at a costume party.
Going trick or treating.
Telling scary stories.
Visiting "haunted" attractions.
Some Christians attend church services or host a light party.
Watch a scary movie.
It's the easiest solution to still get your spooky fix, and doesn't involve you leaving your couch. Win-win.
Binge-watch a season of American Horror Story.
Want something a bit longer than a movie to keep you busy all Halloween long? Turn on a season of the always-creepy American Horror Story for hours of spine shivers.
If you want to do something that requires a bit (just a bit!) more physical activity than watching a movie, pick up a pumpkin and break out your carving knife. You'll get into the Halloween spirit and get an arm workout.
Go bobbing for apples.
This is such an autumn activity, but how many people actually do it? Without trick-or-treating, now you can try!
Hit up a hayride.
Hey, we get it: You want to get out of your house this Halloween. If hayrides are your thing, there's no better night to do it — the window of opportunity is closing as winter approaches.
Or hit up a haunted house.
Another excellent option for a Halloween adventure, because even if it's run by a bunch of teenagers, a haunted house will never fail to make you scream your head off.
Head to a Halloween party — or host one of your own!
If you're afraid of getting scared (we get it), skip the horror and instead celebrate Halloween with a party. If you don't know anyone hosting one, step up to the plate yourself!
Bake a candy cake.
Put an adult twist on Halloween candy with a candy-filled cake recipe. Tasty and it’ll keep you occupied.
Put yourself into a sugar coma.
Baking isn't your thing? Celebrate Halloween the same way you did post-trick-or-treating: by eating an obscene amount of candy (no one said you have to share with trick-or-treaters).
Hand out candy.
Passing along your favorite Halloween traditions to the next generation? Well, there's really nothing sweeter, is there?