But bet you didn't know the true story behind the ancient origins of Halloween.

It all goes back some 2,000 years to the ancient Celtic festival known as Samhain, celebrated on November 1st.

On the night before Samhain, people believed that the dead returned as ghosts.

They would leave food and wine on their doorsteps to keep roaming spirits at bay, and wear masks when they left the house so they would be mistaken for fellow ghosts.

The Christian church turned Samhain into All Saints' Day, or All Hallows, in the 8th century.

The night before became All Hallows' Eve, later shortened to Halloween.

You've heard of trick-or-treating on Halloween, but what about souling, or guising?

All three of these traditions originated in medieval Britain.

On All Souls' Day, November 2nd, the needy would beg for pastries known as soul cakes.

In return, they would pray for people's dead relatives.

This was called souling.

In the medieval Halloween tradition of guising, young people would dress up in costume and accept food, wine, money, and other offerings in exchange for singing, reciting poetry, or telling jokes.

In 19th century America, Irish and Scottish immigrants revived these old traditions.

The result was trick-or-treating.

At first, it was much more about the tricks, in the form of pranks and hijinks, than the treats.

It wasn't until the 1950s that the custom took on its current family-friendly, kid-centered form.

Today, Halloween is big business, with U.S. consumers spending more than $2.5 billion on costumes annually.

Add in the candy, and it's estimated that Americans spend up to $6 billion on Halloween each year, making it the second most commercial holiday after Christmas.

So whether you're a fan of tricks, treats, or trivia, there's a bit of Halloween history.

We bet you didn't know!