This is Twitter.com says about Twitter:

'An information network

Twitter is a real-time information network that connects you to the latest information about what you find interesting. Simply find the public streams you find most compelling and follow the conversations.

At the heart of Twitter are small bursts of information called Tweets. Each Tweet is 140 characters in length, but don’t let the small size fool you—you can share a lot with a little space. Connected to each Tweet is a rich details pane that provides additional information, deeper context and embedded media. You can tell your story within your Tweet, or you can think of a Tweet as the headline, and use the details pane to tell the rest with photos, videos and other media content.