Black Friday
noun
US
: the Friday immediately following Thanksgiving Day that is considered by retailers to mark the beginning of the holiday shopping season
Note: The origin of Black Friday in this sense is not known for certain. The day was allegedly so named either in reference to traffic congestion in central cities on the day after Thanksgiving or to the supposed fact that retailers' accounts shifted from red to black with the beginning of the shopping season.
Word History
First Known Use
1961, in the meaning defined above