What Is Web 2.0

http://www.oreilly.com/pub/a/oreilly/tim/news/2005/09/30/what-is-web-20.html

This article is an attempt to clarify just what we mean by Web 2.0.
In our initial brainstorming, we formulated our sense of Web 2.0 by example:
Web 1.0

Web 2.0
DoubleClick
-->
Google AdSense
Ofoto
-->
Flickr
Akamai
-->
BitTorrent
mp3.com
-->
Napster
Britannica Online
-->
Wikipedia
personal websites
-->
blogging
evite
-->
upcoming.org and EVDB
domain name speculation
-->
search engine optimization
page views
-->
cost per click
screen scraping
-->
web services
publishing
-->
participation
content management systems
-->
wikis
directories (taxonomy)
-->
tagging ("folksonomy")
stickiness
-->
syndication
The list went on and on. But what was it that made us identify one application or approach as "Web 1.0" and another as "Web 2.0"? (The question is particularly urgent because the Web 2.0 meme has become so widespread that companies are now pasting it on as a marketing buzzword, with no real understanding of just what it means. The question is particularly difficult because many of those buzzword-addicted startups are definitely not Web 2.0, while some of the applications we identified as Web 2.0, like Napster and BitTorrent, are not even properly web applications!) We began trying to tease out the principles that are demonstrated in one way or another by the success stories of web 1.0 and by the most interesting of the new applications.