Black Friday has its origins in the United States (Philadelphia) and has been celebrated for decades. The Black Friday tradition arose as the start of Christmas shopping after Thanksgiving. On that day, store accounts went from the red of losses to the black of profits. Although another story tells that the "Black Friday" name comes from the traffic that crowded the streets the day after Thanksgiving.
Black Friday is a sales period that usually takes place on the last Friday in November, the month before Christmas shopping. Over time, many retailers have extended Black Friday to the last weekend in November. Even for the whole week.