Web 2.0 is often referred to as the Read/Write Web. WikiPedia defines this new environment as " a perceived transition of the World Wide Web from a collection of websites to a full-fledged computing platform serving web applications to end users. The proponents of this thinking expect that ultimately Web 2.0 services will replace desktop computing applications for many purposes." http://en.wikipedia.org/wiki/Web_2.0

According to Welcome to Web 2.0--Fryer, http://www.wtvi.com/teks/web2/, the characteristics of (most) Web 2.0 or Read/Write Web tools are:
  1. The web is the platform.
  2. Sharing is inherent to the tool.
  3. Tools facilitate communication and interaction.

Let's take a closer look at Mr. Freyer's excellent website http://www.wtvi.com/teks/web2/

Important Web 2.0 Topics from Welcome to Web 2.0:
  1. Wikipedia http://en.wikipedia.org/wiki/Main_Page
  2. Creative Commons http://creativecommons.org/learnmore

Here's another good video: