"Singles Day" is a shopping bonanza in China

An informal holiday that started off as a student joke in China has grown into what's likely the world's busiest shopping day.

"Singles Day," as it's called, is similar to Cyber Monday in the U. S., but with a completely different twist. The idea is that people who have no significant others in their lives can buy gifts for themselves or for potential love interests.

The holiday takes place on a very lonely looking date: Nov. 11, or "11/11," which has four single ones. Singles Day was created by Chinese college students in the 1990s, the story goes, as a Valentine's Day of sorts for unattached people.

A day devoted completely to shopping was an easy one for retailers to get on board with, and they began offering large discounts and promotions to attract customers. And that's how a "holiday" was born.

This year, Alibaba (BABA) stands to rack up massive sales for Singles Day. It handles about 80 percent of China's e-commerce, after all. Shares of the retailer closed up 4 percent Monday after it said it rang up its first $1 billion in Singles Day sales in just under 18 minutes. It took about an hour to hit that milestone last year.

However, the stock shed 3.3 percent, or $3.90 to $115.25 as of 1:32 p.m. ET Tuesday.

Singles Day is such a big deal for Alibaba that it has rented hundreds of hotel rooms near its headquarters in previous years for its employees to take breaks. It also sets up hundreds of lounge chairs on campus to keep workers rested.

Analysts estimate Alibaba's haul for this year's Single's Day at about $8.2 billion to $9.8 billion, CNBC reports. The company's shares have zoomed 75 percent since the September initial public offering.

The numbers blow away any American shopping day. Cyber Monday sales in the U.S. hit a record $2.3 billion last year, according to Adobe Systems (ADBE), which analyzed 900 million visits to retailers' websites.

Already, reports of extravagant Singles Day purchases are surfacing from China. One Guangzhou programmer spent about $82,000 to buy 99 iPhone 6 devices, which he placed into the shape of a heart on the ground, The Nanfang Insider reports. He proposed to his girlfriend inside the heart, in front of a crowd of onlookers, but maybe he should have found a more private venue instead. She rejected his proposal.