How well retailers fare on Cyber Monday will offer insight into Americans' evolving shopping habits during the holiday shopping season, a time when stores can make up to 40 percent of their annual revenue. With the growth in high speed Internet access and the wide use of smartphones and tablets, people are relying less on their work computers to shop than they did when Shop.org, the digital division of trade group The National Retail Federation, introduced the term "Cyber Monday.""People years ago didn't have ... connectivity to shop online at their homes. So when they went back to work after Thanksgiving they'd shop on the Monday after," said Vicki Cantrell, executive director of Shop.org. "Now they don't need the work computer to be able to do that." As a result, the period between Thanksgiving and Cyber Monday has become busy for online shopping as well. Indeed, online sales on Thanksgiving Day, traditionally not a popular day for online shopping, rose 32 percent over last year to $633 million, according to comScore. And online sales on Black Friday were up 26 percent from the same day last year, to $1.042 billion. It was the first time online sales on Black Friday surpassed $1 billion. For the holiday season-to-date, comScore found that $13.7 billion has been spent online, marking a 16 percent increase over last year. The research firm predicts that online sales will surpass 10 percent of total retail spending this holiday season. The National Retail Federation estimates that overall retail sales in November and December will be up 4.1 percent this year to $586.1 billion But as other days become popular for online shopping, Cyber Monday may lose some of its cache. To be sure, Cyber Monday hasn't always been the biggest online shopping day. In fact, up until three years ago, that title was historically earned by the last day shoppers could order items with standard shipping rates and get them delivered before Christmas. That day changes every year, but usually falls in late December.