What Is Twitter? Twitter is a service for friends, family, and co–workers to communicate and stay connected through the exchange of quick, frequent answers to one simple question: What are you doing?   twitter.com

Why do so many people seem to like Twitter? Simplicity has played an important role in Twitter's success. People are eager to connect with other people and Twitter makes that simple. Twitter asks one question, "What are you doing?" Answers must be under 140 characters in length and can be sent via mobile texting, instant message, or the web.   twitter.com

Twitter is a free social networking and micro-blogging service that enables its users to send and read messages known as tweets. Tweets are text-based posts of up to 140 characters displayed on the author's profile page and delivered to the author's subscribers who are known as followers. Senders can restrict delivery to those in their circle of friends or, by default, allow open access. Users can send and receive tweets via the Twitter website, Short Message Service (SMS) or external applications. While the service costs nothing to use, accessing it through SMS may incur phone service provider fees.   Wikipedia