Millions of people around the world use social media. Social media are the Internet platforms that allow users to create content and share information. The largest services include Facebook and Twitter. LinkedIn focuses on business and career development. Other sites are aimed at younger users. Most people use these sites to form social networks.

In essence, social networks allow individuals to stay in contact with others. Their networks may include friends, family, classmates, and business associates. Social media sites also allow people to link with their friends' friends. In this way, social media differs from the chat rooms that were once the most popular way to interact online. Those forums centered on specific subjects. On social media, users create their own unique forums. They do so by building pages about themselves. The pages may include photos, videos, text, and other information about the user. The user can then link their page to pages of friends.

Different social media sites provide varying degrees of privacy. Some are anonymous. Members use "screen names." On others, members post photos and detailed personal information. Often, social media sites allow users to select different levels of privacy for different levels of contacts.

In just a few years, social media has become wildly popular. As of 2015, Facebook had approximately 1.5 billion active users. It is, by far, the most popular social media site. It is also among the most visited Internet sites of any kind. Twitter and Instagram are next. They each have about 300 million active users. There are hundreds of other such sites with smaller memberships.

The idea of social networking traces to the 1960s. At that time, U.S. psychologist Stanley Milgram found that every American was linked to every other American. Between them was a chain of about six mutual acquaintances. This became known as the "six degrees of separation."

In 1997, sixdegrees.com launched as an early social-networking site. Users posted profiles and friend lists. Everyone could see the names of their friends' friends. Since then, networking sites have become much richer. MySpace was launched in 2003; Facebook followed in 2004. Through these and other sites, social networking spread quickly. They made it easy to share journal entries, photos, video, and other media.

In 2006 a site called Twitter was launched. It limited users to 140-character "tweets." This is far less information than is found on other sites. But tweets can easily be sent to mobile devices. Each member chooses which other members they want to receive tweets from. Twitter has since added the ability to post photos and videos.

Instagram arrived in 2010. It allows users to easily share photos and short videos.

Modern social media depends on two technological advances. The first is sophisticated programming. Behind the scenes, programs continually update member pages. The second is broadband Internet connections. These high-speed connections make it easy to post and view photos, videos, and audio. In the 1990s few people had broadband connections. By 2014 about 70 percent of U.S. households had broadband Internet service.

Many social media sites cater to specific audiences. Some are organized around a common interest, such as cars or sports. Others are aimed at certain age groups.

Politicians and celebrities have tapped into social media. Their friends lists can number in the tens of thousands. Performers use social media to alert fans to upcoming shows. Social media is also useful to social groups. These include sports teams, clubs, and charities. Even when away from the computer, people can remain connected through mobile devices. Instant messaging (IM) also keeps people connected. IM is a type of real-time online chat.

Social media has become a powerful tool for social change. It is often used to raise awareness about important issues. Social media often spurs people to take action. It helps to raise money for charity. And it provides an outlet for people to call on political and business leaders for reform.

Unfortunately, social media has some dangers. Most sites do not verify the information submitted by members. As a result, false identities are common. Children, in particular, can be exploited. In some cases, abuse results when children agree to meet an online friend in person. In other cases, strangers have tracked down children through personal information disclosed online.

Anonymity can provide privacy. But anonymous networking has drawbacks, too. Sometimes it promotes online bullying and taunting. But children are not alone in being victimized. Identity theft can occur when adults disclose too much information.

Because of such dangers, many social media sites have minimum age requirements. They vary by site. It is also important that young users check with parents before using such sites. Experts say that parents should carefully monitor who children are interacting with and what type of information they are sharing. Kids and teens are advised to never agree to meet with anyone that they have encountered online.

Social networking can also prove embarrassing. This is particularly true when people use it to post private information. Such news can easily end up haunting the person who posted it. In addition, downloads from social media sites can carry computer viruses. Posting e-mail addresses can generate spam. Some sites are tackling these issues with security software. But it is an ongoing battle.

Social media continues to transform how people meet and communicate. The Global Positioning System (GPS) is bringing one such revolution. It enables networks to track a member's location.

This has a number of possible uses. For example, a person walking into a crowded room can use social networking applications to immediately determine if any of his or her friends are present. Future developments may make these tools even more powerful.

Clearly, there are privacy concerns in this socially networked world. But, for now, they have not slowed interest.