Media playback is unsupported on your device Media caption Black Friday explained - in 60 seconds

Black Friday is the biggest shopping day of the year in the biggest economy in the world.

Full from their Thanksgiving feasts, millions of US shoppers descend on stores across the country on the Friday after the holiday, hoping to save on their Christmas shopping.

But as ever more promotions proliferate - add Cyber Monday and Small Business Saturday to the shopping calendar - the question remains: Just what is Black Friday anyway?

Here are 10 surprising facts about America's unofficial paean to all things commercial.

1. "Black Friday" used to refer to stock market crashes in the 1800s.

Although it is now known as the biggest shopping day in the US, the term "Black Friday" originally referred to very different events.

"Black for centuries has been used for various calamities," says linguist Benjamin Zimmer, executive editor of Vocabulary.com.

Image copyright Library of Congress Image caption A chalkboard shows the prices of gold on "Black Friday", which reached a high not surpassed for 100 years

In the US, the first time the term was used was on 24 September 1869, when two speculators, Jay Gould and James Fisk, tried to corner the gold market on the New York Stock Exchange.

When the government stepped in to correct the distortion by flooding the market with gold, prices plummeted and many investors lost sizable fortunes.

Image copyright Macy's Image caption Macy's parades began in 1924 and featured store employees

2. "Santa Claus parades" were Black Friday's predecessor.

For many Americans, the Macy's Thanksgiving Day Parade has become part of the holiday ritual.

But the event actually was inspired from the US's neighbours in the north. Canadian department store Eaton's held the first "Santa Claus parade" on 2 December 1905. Once Santa appeared at the end of the parade, the signal was that the holiday season - and thus, holiday shopping, had begun. Of course, consumers were encouraged to buy their presents at Eaton's.

US department stores such as Macy's took inspiration from the parade, and started sponsoring similar efforts across the country. In 1924, New York saw the first Macy's parade featuring animals from Central Park Zoo and run by the store's employees.

3. The date of Thanksgiving was, indirectly, determined by holiday shoppers.

From the mid-nineteenth century to the early twentieth century, in a custom started by US President Abraham Lincoln, the president would declare a "day of thanks giving" on the last Thursday in November. This could either fall on the fourth or fifth Thursday in the month.

But in 1939, a funny thing happened - the last Thursday happened to be the last day in November. Retailers, worried about the shortened holiday shopping season, petitioned then-President Franklin Delano Roosevelt to declare the holiday a week earlier - which he did.

For the next three years, Thanksgiving was known derisively as "Franksgiving" and celebrated on different days in different parts of the country.

Finally, at the end of 1941, a joint resolution from Congress cleared up the matter. From then on, Thanksgiving would be celebrated on the fourth Thursday in November - guaranteeing an extra week of shopping before Christmas.

Image copyright FDR Library Image caption Mr Roosevelt received a barrage of messages protesting his capitulation to the will of retailers

4. 'Friday-after-Thanksgiving-itis'

According to Bonnie Taylor-Blake, a researcher at the University of North Carolina, Factory Management and Maintenance - a labour market newsletter - lays claim to the first use of the term as it relates to the holiday.

In 1951 the circular drew attention to the suspiciously high level of sickness that day.

"'Friday-after-Thanksgiving-itis' is a disease second only to the bubonic plague in its effects. At least that's the feeling of those who have to get production out, when Black Friday comes along. The shop may be half empty, but every absentee was sick - and can prove it," reads the circular.

5. Big Friday?

Image caption A New York Times report from 1975 locates the phrase "Black Friday" as a bit of Philadelphia slang

The city that first popularised the term was Philadelphia. Police officers, frustrated by the congestion caused by shoppers on the day, started referring to it derisively as "Black Friday".

Unsurprisingly, retailers weren't happy to be associated with traffic and smog.

So they tried to rebrand the day "Big Friday", according to a 1961 local Philadelphia paper.

Needless to say, the term didn't stick.

6. "Black Friday" didn't become a national term until the 1990s.

The phrase 'Black Friday' remained a Philadelphia quirk for a surprisingly long time.

"You see it spreading a little bit to Trenton, New Jersey, which is close by, but it doesn't really start getting mentioned outside of Philadelphia until the 1980s," says Mr Zimmer.

"It didn't become widespread until the mid-90s."

7. Some say Black Friday refers to "going into the black".

Retailers tried to put a positive spin on the "black" bit of the term by saying it was when retailers became profitable, or as the saying goes "went into the black". However, there is no evidence to back this claim up.

It is true that holiday sales make up the bulk of consumer spending for the year.

Last year, shoppers on Black Friday spent an estimated $59.1bn, according to the National Retail Federation. But how much of that is profit isn't clear - given how retailers vie with each other to offer bigger incentives and discounts.

8. Black Friday became the biggest shopping day of the year in 2001.

Although it's often touted as the biggest shopping day of the year, the day didn't earn the designation consistently until the 2000s.

That's because, for many years, the rule wasn't that Americans loved deals, it was that they loved procrastinating. So up until that point, it was the Saturday before Christmas that typically saw the most wallets being emptied.

Media playback is unsupported on your device Media caption Samira Hussain looks at how people are spending their cash on Black Friday

9. Black Friday has become an international affair.

Canadian retailers have long winced as their customers went south on Black Friday in search of better shopping deals. So now they've begun offering their own sales - despite the fact that Canadian Thanksgiving is a full month earlier.

In Mexico, there is El Buen Fin, which roughly translates as "the good weekend". It's pegged to the anniversary of Mexico's 1910 revolution, which sometimes falls on the same day American Thanksgiving. It lasts, as the name suggests, the entire weekend.

Beyond North America, as online shopping has grown, retailers like Amazon have looked to Cyber Monday, first heard of in 2005, to promote deals for shoppers across the globe. While in China, the recently launched 'Singles Day' prompted sales of two million bras in one hour, making a pile that would be three times higher than Mount Everest.

10. Black Friday is becoming extinct.

Wal-Mart, the world's largest retailer, broke the Black Friday tradition in 2011, when it opened its store on Thanksgiving evening. Ever since, retailers have been in a race to catch up and now, 33 million Americans said they planned to shop immediately after turkey.

But don't worry - this time, retailers have come up with a name themselves: "Grey Thursday".