What is it? It is a catch-phrase describing the "next generation" of the internet with a learner-centric focus, rather than a classroom-centric focus. It's a hard concept to describe, but I best grasp what Web 2.0 is by comparing how it is different from Web 1.0.
Web 1.0 was about reading the internet, while
Web 2.0 is about writing in the internet.
Web 1.0 involved downloading, while
Web 2.0 involves uploading and downloading.
Web 1.0 was about companies, while
Web 2.0 is about "the people".
Web 1.0 was about passive instruction, while
Web 2.0 is about discussion.
Web 1.0 was about static web pages, while
Web 2.0 is about blogs.
On the Association of American Medical Colleges (AAMC) website, there is a great review of Web 2.0 and the idea of a "Personal Learning Environment". Go to AAMC article.
Figure from the AAMC website article