Micro-blogging is defined as a quick update usually containing a very limited number of characters. It is a popular features of social networks like Facebook where you can update your status, but it has become best known because of Twitter. While Twitter may have started as a micro-blogging service, it is grown into much more than simply a tool to type in quick status updates. So when asked "What is Twitter?", I often describe it as a cross between blogging and instant messaging, though even that doesn't do it justice.