A medium is a means of mass communication, such as television, radio or newspapers. Harold Innis, a leading scholar of communication and media theories, separated media into two categories, time-biased and space-biased. Time-oriented media lasts longer but reaches few, while space-oriented media reaches many but is short-lived. Twitter is a social form of media, sending short messages that have the potential of a large audience on a global scale, fitting into Harold Innis' category of a spatially oriented form of media. As mentioned, Twitter is a social medium that allows its two hundred million users (twitter.com) to send one hundred and forty character long messages, or tweets, to the world. Members "follow" other users whose tweets they want to see on their home feed. By default, tweets are visible to the public, including non-Twitter members, but users have the option to make their tweets private. Users can "retweet" someone else's tweet, which will cause the tweet to be shown to all of the retweeter's followers. Twitter also uses hashtags, which are words or phrases typed after the "#" sign that direct users to other tweets with the same hashtag. The site was launched in 2006 but gained much of its popularity in 2012, when the site surpassed five hundred million members. users. (techcrunch.com) As of September 2013, company data showed that millions of users send four hundred million tweets per day. (theguardian.com) Due to its extreme success Twitter announced that it would be applying for an IPO. Seventy million shares on Twitter were priced at $26 and closed at $44.90 on the first day of trading on the New York Stock Exchange. This valued the company at thirty-one billion dollars. (BBC) Twitter is… at the heart of the paper… that when a culture moves towards spatially biased media, it moves away from temporally biased media, or vice versa. However, Twitter's short exposure time does not limit its potential for influence and power. A phenomenon known as "Twitter revolutions" has emerged, which Twitter is used to organize protest, most notably the 2011 Egyptian revolution. This potential for influence has led to government blockades in some countries. Twitter is a social form of media that falls into Harold Innis's category of a space-oriented media type, because even with its short messages it has the potential to reach a huge audience on a theoretically global scale, but with a period of exposure minimum. Twitter provides an example of how America and similar cultures want to make information available more quickly to more people, but do so by sacrificing the sustainability of the information over time.