The term Web 2.0, first coined by Tim O’Reilly back in 2004, describes a cluster of web-based services with a social collaboration and sharing component, where the community as a whole contributes, takes control, votes and ranks content and contributors. Web 2.0 services include social networking sites, wikis, communication tools, weblogs, social bookmarking, podcasts, RSS feeds (and other forms of many-to-many publishing), social software, and folksonomies. Central to this new Web is the idea of tagging — the adding of keywords to a digital object (e.g. a website, picture, audiofile or videoclip) to categorise it. This activity is effectively subject indexing but generally without a controlled vocabulary.

The following list provides examples of sites which include some form of user-based tagging:

Blogs

Technorati: http://technorati.com

Bookmarks

Delicious: http://del.icio.us

Books

Librarything: http://www.librarything.com

Emails

Gmail: http://mail.google.com

Events

GoingToMeet: http://www.goingtomeet.com

People

Tagalag: http://www.tagalag.com

Pictures

Flickr: http://www.flickr.com

Podcasts

Odeo: http://odeo.com

Videos

YouTube: http://www.youtube.com

Tagging of course is not a new concept, especially to librarians, indexers and classification professionals. What is new is that the tagging is being done by everyone, no longer by only a small group of experts, and that the tags are being made public and shared. This is the concept of Folksonomy.

A folksonomy is a user-generated taxonomy used to categorize and retrieve web content such as Web pages, photographs and Web links, using open-ended labels called tags. Typically, folksonomies are Internet-based, but their use may occur in other contexts. The folksonomic tagging is intended to make a body of information increasingly easy to search, discover, and navigate over time. A well-developed folksonomy is ideally accessible as a shared vocabulary that is both originated by, and familiar to, its primary users.

In contrast, in the realm of the Web, taxonomy can be defined as:

the laws or principles of classification;

controlled vocabulary used primarily for the creation of navigation structures for websites

The development of the Internet and the Web, and of search engines, led to users doing their own searching. In the Web 2.0 environment users are now also doing their own content creation and information management.

Because folksonomies develop in Internet-mediated social environments, users can often discover who created a given folksonomy tag, and see the other tags that this person created. In this way, folksonomy users often discover the tag sets of another user who tends to interpret and tag content in a way that makes sense to them. The result is often an immediate and rewarding gain in the user’s capacity to find related content. Part of the appeal of folksonomy is its inherent subversiveness: when faced with the choice of the search tools that Web sites provide, folksonomies can be seen as a rejection of the search engine status quo in favour of tools that are created by the community.

Folksonomy creation and searching tools are not part of the underlying World Wide Web protocols. Folksonomies arise in Web-based communities where special provisions are made at the site level for creating and using tags. These communities are established to enable Web users to label and share user-generated content, such as photographs (e.g. Flickr), or to collaboratively label existing content, such as Web sites (e.g. Technorati), books (e.g. LibraryThing), works in the scientific and scholarly literatures, and blog entries (e.g. WordPress).