In other words, every time you press the "like" button, for example, you are an "active user" of Facebook. Maybe you have a Twitter news feed on your Facebook account? That makes you an active user of Facebook too. Do you share music with friends? You're an active Facebook user. If you log into your account and use Facebook to leave comments on the Huffington Post website - and your comments are automatically shared on Facebook - then too, you are an "active user," even if you never spend any time on facebook.com. Facebook's definition of "active" is not problematic or strange accounting like Groupon's, and there is no indication that Facebook is trying to defraud investors. Of course, this raises an obvious question: how many users are actually active using a more traditional definition? In fact, Facebook's "like" button, on third party websites or through "Facebook Connect," allows users to be considered by Facebook as "active" in a euphemistic sense of "engaged" rather than how many users are actually using it monthly. Facebook counts as "active" users who visit its website and mobile site. But it also counts all other categories of people who do not click on facebook.com as "active users." The company considers a user active if he or she "takes actions to share content or activity with his or her Facebook friends or connections via third-party websites integrated with Facebook." On the first page of its prospectus selling shares to the public, Facebook pegs its "monthly active users" at a whopping 845 million people. The social network reaches an even more impressive number when it comes to "daily active users": 483 million people. "Think about what that means for their monetization of daily users," Barry Silbert, CEO and director of equity research at SecondMarket IQ, wrote in his blog. "If they click a 'like' button without going to Facebook that day, they can't be sold ads, they don't see any ads, they can't buy any goods or services. All they do is leverage the entire infrastructure to tell all their friends (who may or may not see what they've done) that they like something online. Period." In December, Nielsen, which tracks Internet usage, calculated 153 million unique users on the Facebook website per month in the U.S., while Facebook said in its filing that it had 161 million monthly active users. Assuming Facebook's U.S. traffic accounts for about 19 percent of its business, that means the difference is made up of at least 40 million users out of 845 million that Facebook defines as "active." The company acknowledges that "there are inherent challenges in measuring usage across large populations of online and mobile users around the world," since, for instance, "usage on certain mobile devices may automatically update with our servers periodically without user engagement, and this activity may cause our systems to count such users or related devices as active Facebook users." Also, the company says, this phantom usage accounts for less than 5 percent of the total. These are some big numbers. It's hard to believe that many people click on facebook.com every day, and that's because they don't. These jaw-dropping numbers should come with an asterisk next to them. Strangely enough, Facebook is actually more transparent than some competitors. Google was recently criticized for disclosing only the number of registered users of its Google+ service, which few people use regularly. Twitter has been similarly criticized. At least Facebook tries to count only those people who are engaging with the service in a meaningful way. Facebook, which declined to comment for this column because it is in the so-called quiet period before its IPO, says its numbers "will differ from estimates published by third parties due to differences in methodology." This is not the first time that an Internet company's metrics have come under scrutiny. In one particularly prominent example, this column last year took apart Groupon's discovery of a funny-sounding and misleading accounting metric called Adjusted Consolidated Segment Operating Income, which included various forms of revenue but excluded cost of sales. The Securities and Exchange Commission asked questions and the company abandoned the measure. View all posts Article Tools E-mail Print Recommend Share Back? CloseTumblrDiggLinkedInRedditPermalinkTwitter If you managed to read all 44 pages of Facebook's prospectus, you would find that the company offers a definition of an "active user" that might not be what you expect. Related thematic articles: Copyright law obstacles, retrieving files from Interstellar legal skyways Hamilton proves alcohol relapse Understanding free website promotion tutorial methods EU investigates Samsung's web patent licensing practices Free "How to promote your website" guide.