Web 2.0

Commenting:

The ability to respond to someone’s ideas in line, and engage in a more direct conversation with an author’s ideas. Commenting is a defining characteristic of blogs, and often when one blogger links to another blog article a linkback (or trackback) creates an extremely powerful network effect by notifying the author that you are engaging their ideas. See an example of a trackback below.

Tagging:

Sites like [ del.icio.us]] and Flickr, two companies that have received a great deal of attention of late, have pioneered a concept that some people call “folksonomy” (in contrast to taxonomy), a style of collaborative categorization of sites using freely chosen keywords, often referred to as tags. Tagging allows for the kind of multiple, overlapping associations that the brain itself uses, rather than rigid categories. In the canonical example, a Flickr photo of a puppy might be tagged both “puppy” and “cute”–allowing for retrieval along natural axes generated user activity.

–Tim O’Reilly, “What is Web 2.0?”

Some online applications utilizing tags:

• del.icio.us Social Bookmarking
• Flickr Image Sharing Site
• Steve Museum: The Art Museum Social Tagging Project