What are Social Media and Social Networks? By Howard Greenstein Social Media Consultant, the Harbrooke Group NY Chapter Leader, Social Media Club Consultant to the Bravo Group, Phila. And Harrisburg, PA (CC) 2006 By Howard Greenstein - Non-Commercial, Attribute, Share alike -Some Rights Reserved
Definition of a Social Networking Site according to researcher (and friend) Danah Boyd: http://www.zephoria.org/thoughts/archives/2006/11/10/social_network_1.html
A 'social network site' is a category of websites with profiles , semi-persistent public commentary on the profile, and a traversable publicly articulated social network displayed in relation to the profile.
An example of this is http://www.myspace.com , http://www.linkedin.com/