Sites such as Yahoo have spent countless dollars to organize information into a useful taxonomy. Web 2.0 companies are finding that there is great economy and value in enabling users to dissect and sort information on their own. This process can be as simple as enabling people to add keywords to content, such as news articles, photographs, or Podcasts, a process known as tagging.

Tagging often produces strange, overlapping characterizations with surprisingly beneficial results. Some have called the results a "folksonomy."
—John Jerney, "Web 2.0: tapping collective selfishness to create a revolution," Daily Yomiuri Online, November 8, 2005

Folksonomy is another example of the way in which the web 2.0 attempts to harness the collective intelligence of its users. The word "folksonomy" is a spin on the word "taxonomy" and refers to the collaborative way in which information is being categorised on the web. Instead of using a centralised form of classification, users are encouraged to assign freely chosen keywords to pieces of information or data, a process known as tagging.
—Stephen O'Hear, "Seconds out, round two," The Guardian (London), November 15, 2005

Last week I asked the AIfIA members' list what they thought about the social classification happening at Furl, Flickr and Del.icio.us. In each of these systems people classify their pictures/bookmarks/web pages with tags (e.g. wedding), and then the most popular tags float to the top (e.g. Flickr's tags or Del.icio.us on the right).

Thomas Vander Wal, in his reply, coined a great name for these informal social categories: a folksonomy.
—Gene Smith, "Folksonomy: social classification," Atomiq.org, August 3, 2004