The U.S. holiday shopping season has arrived. Across the country, Americans are swarming retail stores in a yearly event known as “Black Friday.”

Black Friday — the day after America's Thanksgiving holiday — is traditionally the year's busiest shopping day.

It is the time when stores sharply discount high-priced items, including electronics and the latest new toys. The name “Black Friday” signifies retailers' expectations of high sales, as profits were once recorded in account books in black ink, while losses were recorded in red.

Consumer spending accounts for about 70 percent of the U.S. economy. Some retailers say end-of-the-year holiday spending accounts for about a quarter of their annual sales.

But this year, holiday sales are expected to increase by a smaller amount than they did last year.

At fault is the struggling U.S. economy, with more than 12 million workers still unemployed in the aftermath of the recession in 2008 and 2009. Many Americans are also concerned about the so-called “fiscal cliff” — more than $600 billion in automatic tax increases and spending cuts that go into effect January 1, unless President Barack Obama and Congress can reach a budget agreement.

Stores typically open for Black Friday at midnight. But “Gray Thursday,” a trend that began last year, now has some stores offering a Thursday evening start to the traditional post-Thanksgiving holiday shopping season. Retailers are traditionally closed on Thanksgiving, known for its family gatherings and turkey feasts.

Employees of some chain stores have circulated online petitions pleading with the public to “save Thanksgiving” and stop the Thursday openings so that employees can enjoy their Thanksgiving holiday.

Many retailers are also taking part in “Cyber Monday,” a day of big online shopping discounts.