The indefatigable American consumerist machine feeds on one thing, and one thing alone: Bargains. Bargains power American spending the same way coal powers railroads, particularly this time of year as Christmas approaches. Buying gifts for an entire family, it turns out, is expensive, so consumers demand value. Retailers respond. First it was “Black Friday.” Then, with the advent of online shopping, came “Cyber Monday.” It wasn’t enough, so retailers then decided “hey, why not start black Friday on Thursday?” And so the consumerist beast was sated, if only temporarily.

No more. Enter the newest shopping holiday event, “Green Monday.”

Green Monday is, ostensibly, a shopping day indistinguishable from other event-based online sales. Held on the second Monday in December, Green Monday was created by eBay in 2007 after it experienced one of its highest online shopping days during the month of December. Since its creation, retailers like Walmart, Best Buy and JCPenney have promoted additional sales.

For Walmart Green Monday is especially important, as the world’s largest retailer is attempting to become a powerhouse among online retailers. Joel Anderson, president and CEO of Walmart.com, tells Fortune that the company’s efforts at online-offline synergy are starting to pay off. “Mobile visits made over 50% of the visits to Walmart.com,” he says. In addition, Anderson has noticed more consumers using their mobile devices to check prices and reviews while in physical Wal-Marts as well as order online and pick up at a brick-and-mortar location.

On their obnoxiously SEO-heavy Green Monday landing page, Walmart promises deals across their full suite of product offerings, as well as free shipping on “many” purchases.

Green Monday is defined by business research organization comScore as the Monday with at least 10 days prior to Christmas. In 2009, $854 million was spent online in the US on Green Monday, with sales in 2011 reaching $1.133 billion.

The American consumerist machine is, truly, insatiable.