All these definitions were arrived by using a Web 2.0 tool called Twitter. My network of friends were very generous to offer their perspectives on Web 2.0.
My favorite word for defining Web 2.0 is "collaborating." Web 2.0 is about using collaborative technologies like wikis, nings, social networks, google docs, etc.
It is about sharing and learning together - students to students, teachers to teachers, teachers to students, AND even students to teachers!