Twitter asks the question,
“What are you doing?” and allows you to send a small update (limited to just 140 characters) to your followers. The concept is amazingly simple and that is perhaps one of the main reasons why it has caught on like wildfire. The restriction to 140 characters has resulted in Twitter being labeled “micro blogging”. A traditional blog is a log of what somebody is up to, but in a richer, more detailed format. One of the key benefits of Twitter is that you can send and receive updates (also called tweets) via your browser, email , instant messaging clients and SMS so you can
keep in touch no matter where you are.