Black Friday is the day after Thanksgiving and is generally considered the beginning of the holiday season. The term "Black Friday" was popularized in the early 2000s by online sales websites to compete with physical store sales. As the term spread across the country via the Internet, traditional retailers officially adopted the term as well.
What is Black Friday? BBC News
In the US, Thanksgiving Day is the fourth Thursday in November. The following day, Black Friday, is the most popular shopping day of the year, with many retailers reserving their biggest discounts and best sales for that specific day.
The name is also linked to the term "in the black", which stands for profit in the accounts. Many retailers operate at a loss (in the red) for most of the year and make a profit during the holiday season in November and December.
Beginning in 2013 and 2014, more and more retailers began moving the start time of their Black Friday deals from the early morning hours of Friday morning to the evening of Thanksgiving Day in order to extend the popular shopping day. Some retailers went even further and started their Black Friday sales on the Monday before Thanksgiving Day.