Today is the unofficial first day of the holiday shopping season. Here are five facts you should know about “Black Friday.”

1. The term “Black Friday” was coined by the Philadelphia Police Department’s traffic squad in the 1950s. According to Philadelphia newspaper reporter Joseph P. Barrett, “It was the day that Santa Claus took his chair in the department stores and every kid in the city wanted to see him. It was the first day of the Christmas shopping season.” Barrettt first used the term in the city’s newspaper, the Evening Bulletin, in 1961 to refer to the traffic problems on that day. Local plained to missioner Albert N. Brown about the negative association of the term, so Brown released a press release describing the day as “Big Friday.” By then it was too late; the media had already started referring to the day after Thanksgiving as “Black Friday.”

2. Because so few people were aware of the origin of the term Black Friday, analternative explanation became popular: that it is the day on which retailers finally began to show a profit for the year (in accounting terms, moving from being “in the red” to “in the black”). The earliest use of this meaning, though, dates only to the early 1980s.

3. The predecessor to “Black Friday” was the “Santa Claus parade.” Canadian department store Eaton’s held the first Santa Claus parade on December 2, 1905. Santa’s appearance at the end of the parade signaled that the holiday season — and Christmas shopping — had begun. In the U.S., the department store Macy’s adopted the idea and started sponsoring similar parades across the country. The most famous event, the Macy’s Thanksgiving Day parade in New York City, began in 1924.

4. For several years in the 1930s, the date of Thanksgiving was moved to increase the Christmas shopping period. At the request of retailers, Franklin D. Roosevelt agreed to move his holiday proclamation up one week to the fourth Thursday in November. Of the then-48 states, 32 joined Roosevelt in the “Democratic Thanksgiving” while 16 stuck with the “Republican Thanksgiving” of the traditional date. After plained about “Franksgiving,” Roosevelt signed legislation making Thanksgiving a legal holiday on the fourth Thursday in November.

5. In 2009, K-Mart became the first major national retailer to open its stores on Thanksgiving morning. Several other large retailers—including Wal-Mart, Sears, and Toys R Us—also began opening their stores a day early in 2011. Since then, BlackFriday has been replaced by what some retailers refer to as “Grey Thursday.”