Black Friday is the day following Thanksgiving Day in the United States, traditionally the beginning of the Christmas shopping season. Depending on the source, the term dates either from the 1980s or back as 1966, although its usage was primarily on the East coast. The term has become more common in other parts of the country since 2000. On this day many U.S. retailers open very early, with most of the retailers typically opening at 5AM or even earlier, at midnight.
The day's roots may have originated in Philadelphia, where it was used to describe the heavy and disruptive pedestrian and vehicle traffic which would occur on the day after Thanksgiving. Others claim it was part of mid-1980s anti-consumerism backlash, when people took a pledge to "blackout" that day - staying home, rather than shopping.
I'd rather be drawn and quartered than to go anywhere near a mall on this day.
Steely Dan 'Black Friday' 1975