The Definition of Social Media - Brian Solis
"1 - social media describes the online tools that people use to share content, profiles, opinions, insights, experiences, perspectives and media itself, thus facilitating conversations and interaction online between groups of people. These tools include blogs, message boards, podcasts, micro blogs, lifestreams, bookmarks, networks, communities, wikis, and vlogs.
A few prominent examples of social media applications are Wikipedia (reference), MySpace and Facebook (social networking), Twitter and Jaikue (presence apps), YouTube (video sharing), Second Life (virtual reality), Upcoming (Events), Digg and Reddit (news aggregation), Flickr and Zooomr (photo sharing), Blogtv, Justin.tv, and Ustream (livecasting), Stickham, YourTrumanShow (episodic online video), Izimi and Pownce (media sharing), del.icio.us (bookmarking) and World of Warcraft (online gaming).
2 - Social Media is the democratization of content and the understanding of the role people play in the process of not only reading and disseminating information, but also how they share and create content for others to participate. It is the shift from a broadcast mechanism to a many-to-many model, rooted in a conversational format between authors and people."