Black Friday, Small Business Saturday, and Cyber Monday are about accumulating stuff.

Giving Tuesday is about giving back.

Tuesday is the third Giving Tuesday, a day dedicated to charitable giving throughout the world.

Ever since Americans started assigning particular days after Thanksgiving to shopping, many social-minded citizens have become repulsed by what they've perceived as rampant acquisitiveness.

Before yet another day became the sole provenance of commerce, New York's 92nd Street Y, along with the United Nations Foundation, appropriated the Tuesday after Thanksgiving for altruists.

"It's a day for giving to nonprofit organizations," said Asha Curran, a director at the Y, a nonprofit cultural center where the idea for Giving Tuesday was germinated. "We're thrilled it's grown."

On the first Giving Tuesday in 2012, the number of online donations to nonprofits increased by half over the same day in 2011, Curran said. Between 2011 and 2013, there was a threefold increase, she added.

The number of organizations involved in Giving Tuesday rose from 2,500 in 2012 to 10,000 this year in America and abroad, Curran said. She said that the effort's decentralized nature makes it impossible to determine how much money was raised by the many participants.

What appeals to people, observers say, is the day's unstructured nature. Celebrating the power of giving without an overarching entity running it, Giving Tuesday is an egalitarian phenomenon, participants believe.

While there is a GivingTuesday.org, the website describes the movement's origins and philosophy, but notably does not accept any money.

"It's inventive and easy to get people to stop thinking about consuming so much," said Eileen Heisman, president and CEO of the National Philanthropic Trust in Jenkintown.

Local companies such as Comcast, Independence Blue Cross, the Eagles, and dozens of others have participated by donating to nonprofits in the area, Heisman said.

Corporations worldwide, including Microsoft, Hyatt Hotels, H&M, and many others have partnered to give to charities on Giving Tuesday, which is sometimes represented as #GivingTuesday.

A lot of the word of the good works of the day is spread via social media, which makes it popular among millennials like John Mauricio Lyons.

A West Philadelphia financial counselor, Lyons, 27, will give $50 to $100 on Tuesday to the Spruce Foundation, which awards grants to organizations that work with low-income youth in Philadelphia.

"It's important for me to give because there's not a lot out there for a lot of folks," Lyons said. "Although the economy has improved, a lot of people have been left behind."

Not everyone supports Giving Tuesday.

Laura Otten, executive director of the Nonprofit Center at La Salle University, said Giving Tuesday "flies in the face of good philanthropy," which depends on cultivating enduring relationships with donors over a long period of time - not on a quick-hit appeal.

Giving shouldn't be a one-day effort, but an ongoing flow based on mutual trust, Otten said. And, she added, giving "shouldn't be about assuaging guilt for spending too much on Black Friday."

Katherina Rosqueta, executive director of the Center for High Impact Philanthropy at the University of Pennsylvania, said some believe that dedicating a single day to giving risks so-called donor fatigue. That's when people who are typically solicited for money feel over-asked.

Perhaps, then, Giving Tuesday could be "a day to thank the folks who've been supporting the nonprofits all along," rather than a day of charitable solicitation, she said.

Certainly, people should be thinking about helping the less fortunate all year, said Linda Samost, founder of Sunday Suppers, a Hunting Park-based nonprofit providing meals and food education.

"But," she added, "this is not reality."

So it helps to set aside a Tuesday to focus people's attention, she said.

Nonprofits in the Philadelphia area embrace the day as a chance to get out the word about their work.

"For us, Giving Tuesday is a tremendous opportunity to raise awareness," said Laura Wall, executive director of the Greater Philadelphia Coalition Against Hunger.

The day offers a "great confluence of those who are able to help and those who need it," said Phoebe Kitson-Davis, program manager of the Chester County Food Bank in Exton. "We are the grateful go-betweens."

At Philabundance, the hunger-relief agency serving the Philadelphia region, including portions of South Jersey, "we ask our followers on Twitter and Facebook to donate whatever they can," said spokeswoman Lindsay Hughes.

A few Giving Tuesday activities try to combine charity with fun.

The Philadelphia Orchestra is asking its audience at a free concert at the Kimmel Center to contribute to Cradles to Crayons, which helps low-income children.

And the Food Trust, a nonprofit that offers people access to healthy food, is partnering with three Philadelphia restaurants - the Farm and Fisherman, Tria Cafe, and Pitruco Pizza - that promise to donate 30 percent of evening food sales on Tuesday to the organization.

"After the hustle and bustle of the shopping weekend," said Ryanne Jennings, Food Trust spokeswoman, "we try to shine the spotlight on giving back."

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