Black Friday is the day following Thanksgiving Day in the United States, traditionally the beginning of the Christmas shopping season. On this day, most major retailers open extremely early, often at 4 a.m., or earlier, and offer promotional sales to kick off the shopping season, similar to Boxing Day sales.
Black Friday is popular as a shopping day for a combination of several reasons. As the first day after the last major holiday before Christmas it inaugurates the Christmas season. Additionally, many employers give their employees the day off as part of Thanksgiving leave, increasing the potential number of shoppers. In order to take advantage of this, virtually all retailers in the country, big and small, offer various sales. Recent years have seen retailers extend beyond normal hours in order to maintain an edge, or to simply keep up with competition. Such hours may include opening as early as 12:00 a.m. or remaining open overnight on Thanksgiving Day and beginning sales prices at midnight.
As of 2009, Black Friday has been spreading accross Canada, specially in Ontario and the southern provinces, providing great discounts as a mean to discourage customers to cross the border to benefit from this special Shopping Day. Of course this is great news, as it means more big sales and savings for us!
Source: Wikipedia - Black Friday (Shopping)