Millions of Americans are heading to airports or taking to the nation's highways to visit friends and relatives in advance of Thursday's Thanksgiving holiday.

The holiday is engrained in American life as a day for family gatherings with sumptuous turkey feasts with a wide array of side dishes and pies. By one estimate, more than 43 million people are expected to travel 80 kilometers or more to attend holiday gatherings between Wednesday and Sunday.

But other Thanksgiving traditions are prominent in the U.S. as well, including religious services and key youth and professional football games. One major retailer, the Macy's department store chain, stages a splashy parade in New York, with large inflated cartoon balloons and marching bands.

The first American Thanksgiving occurred in 1621, with early North American settlers commemorating a harvest after a harsh winter.

More than a century later, the nation's first president, George Washington declared it a national holiday in 1789. The current U.S. president, newly re-elected Barack Obama, was set Wednesday to follow tradition and “pardon” two turkeys, nicknamed Cobbler and Gobbler. The White House said the birds would then get to live out their days at George Washington's nearby Mount Vernon estate.

The American Thanksgiving, by law celebrated on the fourth Thursday of November, also serves as somewhat of a respite from the commerce of the approaching holiday shopping season, leading to Christmas on December 25.

But that no-shopping-on-Thanksgiving tradition is fading in the U.S., with some chain stores planning to open their doors for early holiday gift-buying on Thursday night. That is just hours ahead of what is called Black Friday in the U.S., traditionally one of the biggest shopping days of the entire year.

In part, the day has been called Black Friday because of the millions of shoppers and traffic congestion throughout the country, from its largest cities to small towns. But the term is also said to describe the day in which retailers have enough sales to be profitable, to put them in the black, in accounting terms.

Consumer spending accounts for about 70 percent of the U.S. economy and some retailers say end-of-year holiday spending accounts for about a quarter of their annual sales. But sales this year could increase just 2.5 percent compared to 2011, according to one estimate.

Holiday sales could be hurt by the sluggish pace of the U.S. economy, with more than 12 million workers still unemployed in the aftermath of the recession in 2008 and 2009.

One other complication is that the White House and Congress are also facing contentious government spending and tax issues that could further hurt the economy if left unresolved in the waning weeks of 2012. Almost all American workers face tax increases January 1 if the dispute is not resolved by the end of the year.