a.k.a. collaborative tagging, social classification, social indexing, social tagging
Modern jargon that refers to an online social network which is a "taxonomy" of knowledge organized by ordinary "folks." Coined by Thomas Vander Wal, it is a system of classification derived from the practice and method of
collaboratively creating and managing tags to annotate and categorize
In other words, regular people like you and I are building networks of knowledge based on common interests by combining "what they know" with "who they know." The topics are all over the map! One way to think of it is like a job board or classified advertising blast but instead the vehicle is a Web site.