It is said to refer to the day that retailers start going into profit - or the black in accounting speak. However, the name has not alway had such positive connotations.
The nickname is first said to have been used by the Philadelphia police department in 1966 who saw it as a "black" day because of the chaos created by people flocking to shops in search of bargains.
The later explanation came about as traders and retailers decided they needed one of their most important shopping days to be seen it a better light.
By the early 1980s, the story behind the name had been spun into the current one - that it was the time when retailers who traditionally operated at a financial loss for most of the year start to go into profit.
Many US retailers open very early on "Black Friday", often at 5am, and offer promotional sales to kick off the shopping season. Although this year, with consumer cutting back struggling retailers have been offering 'Black Friday' deal for weeks and some stores even opened late on Thanksgiving Day to get a jump on rivals.
Of course if sales go badly this year, the name may start to have a more ominous meaning.