It might seem like a gimmick, but "Cyber Monday," just a few years old, is actually an important day for online retailers as they offer one-day discounts to lure holiday shoppers.

"Cyber Monday" has been around since 2005, when shop.org coined the term after figures showed an increase in sales on the Monday after Thanksgiving.

"They did notice a spike in sales first, and then the term was coined," said Dr. Charles Wood, a professor at Notre Dame's Mendoza's College of Business.

Since then, the day has become an important one for those doing business online.

"Today is probably the most important day for online retailers of any shopping day of the year," said Wood.

Numbers are looking strong from Black Friday, Wood said. But shopping on Saturday and Sunday looks to be "way down" from last year, according to Wood. That's why retailers are focused on "Cyber Monday."

"They're worried actually that they'll have negative growth, in November and December, and that's what makes Cyber Monday so important to get these people in there because the negative growth is going to kill some of these companies," said Wood.