The term " Web 2.0 " refers to a perceived second generation of web development and design , that aims to facilitate communication , secure information sharing , interoperability , and collaboration on the World Wide Web . Web 2.0 concepts have led to the development and evolution of web-based communities, hosted services , and applications ; such as social-networking sites , video-sharing sites , wikis , blogs , and folksonomies . – Wikipedia 3/19/09
Twitter is ranked as one of the 50 most popular websites worldwide … a February 2009 Compete.com blog entry ranked Twitter as the third most used social network  based on their count of 6 million unique monthly visitors and 55 million monthly visits.  In March 2009, a Nielsen.com blog ranked Twitter as the fastest-growing site in the Member Communities category. Twitter had a monthly growth of 1,382 percent … followed by Facebook with an increase of 228 percent. 
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.