Black Friday 2016
This year Black Friday 2016 falls on November 25
For tech fans, the Black Friday deals period is bigger than Christmas: it's the day, weekend and increasingly week when electronics retailers go crazy and slash the prices of pretty much everything.
Black Friday has been a big deal in America for decades, but it didn't really take off in the UK until 2013, largely because the Walmart-owned ASDA chain went crazy for it.
But in 2015 ASDA decided not to take part - and firms that did, such as Tesco and Currys, found their shelves largely empty. After a blockbuster Black Friday 2014, many retailers found that Black Friday 2015 didn't live up to their expectations - and many shoppers found that the bargains they found weren't anywhere near as exciting as they'd hoped.
Has the Black Friday boom turned to bust already, or will Black Friday still be Gadget Christmas?
When and what is Black Friday?
Black Friday is the Friday immediately after Thanksgiving, so Black Friday 2016 will fall on the 25th of November.
It's when the US holiday shopping season really kicks off, and it's usually marked by "doorbuster" bargains that cause the kind of shopper misbehaviour that ends up on YouTube.
While it started as a US-only event the global reach of American companies - Amazon, Walmart and so on - has brought Black Friday and its doorbusters to shoppers worldwide.
These days Black Friday is largely an online event, with UK online sales up by 36% year on year to £1.1 billion on Black Friday 2015.
BT Expedite reports that UK retailers received 16.5% more orders over the Black Friday period in 2015 than they did in the same period in 2014, and revenues were up by 19%. However, it also noted that many retailers achieved sales boosts by making Black Friday last longer than a few days.
Amazon's fortnight of deals was longer than most but spreading deals over a week rather than just Black Friday and the following Monday, Cyber Monday, was a key retail trend in 2015.
Are Black Friday deals bad for business?
For consumers, Black Friday is brilliant because it happens just before Christmas and crashes prices at the perfect time. For retailers, though, it's more problematic: is it really wise to slash prices at the beginning of the busiest shopping period of the year?
Many retailers and retail analysts say that it isn't wise at all. When marketing experts Verdict Retail analysed the effect of Black Friday and Cyber Monday 2014, they found that there was "no evidence that it stimulated demand"; by discounting their products, retailers sold stuff they would have sold anyway but for less money.
Consumer spending isn't infinite, so if we splurge our Christmas cash on Black Friday bargains we won't be back to buy more profitable things in December.
That's led retailers such as UK shopping giant John Lewis to say "we've got to ask if it's right to concentrate trade so much in that one period", and other retailers such as Next and Jigsaw decided not to take part in Black Friday 2015.
Some analysts feel the event has distorted Christmas spending, pulling it forward at a time when retailers traditionally charged full prices.
James Miller, senior retail consultant at Experian Marketing Services, told the BBC that "there is little doubt Black Friday has dramatically changed the way people shop in the run-up to Christmas and has created an expectation of deep discounts that arguably did not exist before," while a report by LCP Consulting found that nearly one-third of UK and US retailers believe that Black Friday is "unprofitable and unsustainable."
Black Friday may be a big deal online, but it doesn't seem to be very good for high street shopping.
Research by shopping analysts Springboard and Footfall reported falls in high street shopper numbers of 4.5% and 4.0% respectively.
The fall in footfall might also be due to the relatively restrained nature of Black Friday 2015, which didn't have the panicky discounting that caused fisticuffs in shops the previous year; some shoppers may have stayed at home because the bargains weren't big enough, while others may have been put off by the possibility of getting punched.
Black Friday 2016: the cost of missing out
ASDA may have brought Black Friday to the UK, but it decided not to take part in 2015. Instead, it planned to offer a more sensible discount programme over the Christmas shopping period.
The results? Like for like sales in the 13 weeks to January 1 were down 5.8%, the firm's worst quarterly sales ever. ASDA said that roughly one third of that decline was due to its own discounts, and that 0.4% was due to not taking part in Black Friday. 0.4% doesn't sound like much, but when your quarterly revenues are measured in billions it represents a large sum of money.
Even retailers that do take part in Black Friday can find themselves losing money. In 2014, many UK retailers' websites experienced the equivalent of Denial of Service attacks as bargain-crazed browsers crashed their servers.
The same happened again in 2015, albeit on a lesser scale, with websites such as Tesco.com buckling under the demand. That's an expensive problem, because if people can't access your website they can't buy anything.
John Lewis reported that on Black Friday it would be selling £45 million worth of goods via its website, so just one minute of downtime would cost it £75,000 in lost sales.
Black Friday 2016: what to expect
When you look at the retailers who don't like Black Friday, they tend to have the same thing in common: they aren't electronics and gadget businesses.
Those retailers generally had a brilliant Black Friday in 2015, and there's no reason to think they won't be offering door-busting bargains again in 2016. The discounts will be carefully planned and negotiated with suppliers in advance - retailers learned their lesson in 2014, when they lost a fortune slapping discount stickers on everything in sight - but they'll still be there.
You'll also see fewer websites falling over like fainting Victorians, because after a couple of years of experimentation the big retailers now have a better understanding of how Black Friday demand works - so they know that there's a big surge of demand at midnight and another first thing in the morning, and can plan accordingly.
It's not just the retailers that need to plan, though. We do too: like any big sales event we'll see all kinds of exciting deals, but a bargain's only a bargain if it's something you actually want. Otherwise you're just helping a shop shift surplus stock.
If you know what you want, know what it's worth and are flexible on the details - so for example you want a TV with X features and a screen this big, but you don't care whether it's Samsung or Sony - then you're perfectly placed to bag a Black Friday bargain on Black Friday 2016.