Popular Web Sites Image Gallery
Popular Web Sites Image Gallery

Reid Hoffman, LinkedIn founder and chairman, poses for a picture at the business networking company's headquarters in Mountain View, Calif. See more pictures of popular web sites.

AP Photo/Tony Avelar

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If you've updated your Facebook status, posted photos of last night's party to Flickr for your friends to see or made a business contact through LinkedIn, then you've used a social networking site. But what exactly is a social networking site? What are the key attributes that set it apart from other Web sites? How do they allow people to form online communities and share social networking information?

Some of the earliest sites that we would recognize as being similar to today's social networking sites appeared in the mid 1990s, when the Internet started growing in popularity. These early sites focused on letting users reconnect with people they had known in the past, or finding out how they were connected to other site users.

Friendster appeared in 2002 and followed a similar model, but it offered additional features like photo sharing and it quickly became the first of the "big" social networking sites. Since then, however, Friendster has declined in popularity and is no longer one of the top 20 social networking sites in the United States [source: Hitwise]. After Friendster came MySpace and Facebook, along with sites like Bebo, Hi5, Orkut and Yahoo! 360. In addition, dozens of sites catering to very specific regions or tastes have sprung up. Whether you're interested in books, video games, music or meeting people from Denmark, there's probably a social networking site for you.

The idea of an online community goes back much farther than the 1990s, however. Very early forms of the Internet were used to foster social networks. The earliest online communities were dial-up bulletin-board systems (BBSes) such as The Well and numerous other regional systems. While these early communities did not have the features users have come to expect of modern social networking sites, they shared the core idea of connecting people with common interests.